Rear suspension controller

ABSTRACT

When a sporadic shock due to a protrusion or dip of a road surface is detected at front wheels of a vehicle during its cruising on the road surface, the characteristic of the rear wheel suspension of the vehicle is altered immediately or just before the rear wheels pass it to improve the controllability and the stability of the vehicle or the smooth feeling of the ride. For that purpose, a rear suspension controller is invented which includes a height sensor for detecting the distance between the body of the vehicle and each of the right and left front wheels thereof, height data calculator which generates a plurality of height data from the front vehicle height, a judgement section which compares each of the height data with a respective reference value that is predetermined corresponding to each height datum and generates comparisons and a rear suspension characteristic alteration devices which alter the spring constant, damping force, etc. of the rear suspensions. The height data calculator extracts substantial data from the front vehicle height signal which represents the shape of the bump or dip for judging adequately when to alter or return the rear suspension characteristic.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rear suspension controller for avehicle, particularly to a rear suspension controller which is effectiveagainst a single shock caused by a bump or a dip of a road surface onwhich the vehicle is running.

2. Prior Art

Conventionally, the spring constant, damping force, bush characteristicor stabilizer characteristic of each of various suspension componentsprovided between a body of a vehicle and its wheels is altered undercontrol depending on conditions of a road surface .[.of.]. .Iadd.or on.Iaddend.running conditions of the vehicle in order to prevent thevehicle from being shocked or vibrated and maintain the controllabilityand the stability of the vehicle. For example, altering the springconstant of the air spring of a suspension depending on conditions ofthe road surface, altering the damping force of a shock absorber, andsimply making the characteristic of a bush or a stabilizer variable wereproposed in the published unexamined Japanese patent applications Nos.sho 59-23712 and sho 59-26638, in sho 58-30542 and sho 59-23713, and inthe published unexamined Japanese utility model application Nos. sho59-129613, sho 59-132408 and sho 59-135213, respectively. In suchcontrol, when it is detected by a vehicle height sensor that the vehicleis running on a rough road or when it is detected by a brake sensor oran accelerator sensor that the front of the vehicle has gone up or down,the characteristic of each suspension of the vehicle is altered tomaintain a good controllability and stability of the vehicle running onthe rough road, or to prevent the front of the vehicle from going up ordown further. However, under the above-mentioned conventional control,the vehicle is not judged to be running on a rough road, until a largeturbulence is continuously detected by the vehicle height sensor. Whenthe vehicle is judged to be running on a rough road, the springconstants of the suspensions for all the wheels of the vehicle or thedamping forces of the shock absorbers for all the wheels are increasedto produce a desired effect. If the vehicle passes over a joint of roadpatches or a single bump or dip, the vehicle usually receives only oneshock and resumes running on a flat part of the road again, so that thecharacteristic of each suspension is not altered. For that reson,passengers of the vehicle are not protected from an unpleasant shock dueto such single bump or dip, which is different from the case that thevehicle is running on a rough road having continuous bumps or dips. Insome cases of passing over such single bump or dip, the controllabilityand the stability of the vehicle deteriorate as well.

SUMMARY OF THE INVENTION

The first object of the present invention is to appropriately controlsuspensions provided between a body of a vehicle and its rear wheels, tokeep the controllability and the stability of the vehicle good andprovide passengers of the vehicle with smooth ride.

The second object of the present invention is to alter thecharacteristic of rear suspensions of a vehicle running over such asingle bump or dip of a road surface like a joint of road patches tomaintain the controllability and the stability of the vehicle and thesmooth feeling of the ride.

The third object of the present invention is to alter the characteristicof rear suspensions depending on the vehicle speed as well as the sizeof a bump or a dip to adequately deal with the shock caused by the bumpor dip.

The fourth object of the present invention is to finely alter thecharacteristic of rear suspensions depending on the conditions ofpassing a bump or dip which the front wheels are detected.

The fifth object of the present invention is to control timing for thealteration of the rear suspension characteristic in order to preventunnecessary alteration unless the rear wheels pass the bump or the dip.

The last purpose of the present invention is to apply theabove-mentioned control not only to one type of suspension but also toother various types of suspensions.

According to the present invention, a rear suspension controller for avehicle having suspensions between the body of the vehicle and its rearwheels includes the following means in order to attain the objects:

a front vehicle height detector (e) by which a distance between thefront wheel and the vehicle body is detected to generate a front vehicleheight signal;

a height data calculation means (f) which generates plurality of heightdata from the front vehicle height signal;

a judgement means (g) which compares each of the height data with areference value that is predetermined corresponding to each height datumand generates a judgement result signal depending on the results of thecomparisons;

a rear suspension characteristic alternation means (h) which alters thecharacteristic of the rear suspensions in receiving the judgment resultsignal.

The rear wheel suspension controller may further include a vehicle speeddetector (M1) which detects the speed of the vehicle to generate avehicle speed signal and

a reference alteration means (M7) which alters the reference valuesdepending on the vehicle speed signal. While the front vehicle heightsignal indicates the distance between the body and the front wheel, theheight data is calculated from the front vehicle height signal as, forexample, the displacement of the front vehicle height signal from theaverage value of it or those consisting of one among a displacement ofthe vehicle height signal from the average thereof, a speed of thedisplacement and an acceleration of the displacement and an amplitude ofthe displacement.

Each reference value corresponding to respective height datum may be aplurality of values and the judgment means then generates a plurality ofjudgment result signals depending on the results of the comparisonsbetween the height data and the respective reference values and the rearsuspension characteristic alteration means alters the characteristic ofthe rear suspensions in a plurality of states in response to thejudgment result signals.

The rear suspension characteristic alteration means alters the rearsuspension characteristic either immediately on receiving the judgmentresult signal or a definite time, or a delay time, after receiving it.The delay time is calculated depending on the vehicle speed so that thetiming of the rear suspension characteristic alteration may coincidewith that of rear wheels passing the bump or dip which the front wheelhas passed and detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an outline of the first and second embodiments of thepresent invention.

FIG. 2A shows a schematic figure of a vehicle passing a small bump and alarge bump of a road surface explaining the first and secondembodiments.

FIG. 2B shows time charts corresponding to the explanation of FIG. 2A.

FIG. 3 shows details of the constitution of the embodiments.

FIG. 4 shows a sectional view of a main part of an air suspension.

FIG. 5 shows a sectional view along a line V--V shown in FIG. 4.

FIG. 6 shows a construction of an electronic control unit (ECU).

FIG. 7 shows a construction of an input section which receives a digitalfront vehicle height signal.

FIG. 8 shows a construction of an input section which receives an analogfront vehicle height signal.

FIG. 9 shows a time chart explaining the first and the second judgmentconditions of the first embodiment.

FIGS. 10A, 10B, 10C, 10D, and 10E show flowcharts of process stepsexecuted by the ECU in the first embodiment.

FIG. 11A shows a schematic figure of a vehicle passing a small dip of aroad surface in the first embodiment and FIG. 11B shows timing chartscorresponding to FIG. 11A.

FIG. 12A shows a schematic figure of a vehicle passing a large dip of aroad surface in the first embodiment and FIG. 12B shows timing chartscorresponding to FIG. 12A.

FIG. 13A shows a schematic figure of a vehicle passing a small dip and asubsequent large dip of a road surface in the first embodiment and FIG.13B shows timing charts corresponding to FIG. 13A.

FIGS. 14A, 14B, 14C, 14D and 14E show flowcharts of process stepsexecuted by the ECU in the second embodiment.

FIG. 15 shows timing charts about a vehicle passing a small dip of aroad surface in the second embodiment.

FIG. 16 shows timing charts about a vehicle passing a large dip of aroad surface in the second embodiment.

FIG. 17 shows an outline of the third embodiment of the presentinvention.

FIGS. 18A, 18B, 18C, 18D, 18E and 18F show flowcharts of process stepexecuted by the ECU in the third embodiment.

FIG. 19 shows a relationship between a reference value of the firstdetection process steps and the vehicle speed.

FIG. 20 shows a relationship between a reference value of the seconddetection process steps and the vehicle speed.

FIGS. 21A, 21B and 21C show time charts corresponding to three cases ofthe third embodiment.

FIG. 22 shows an outline of the fourth and fifth embodiments of thepresent invention.

FIG. 23A shows a schematic figure of a vehicle passing a bump of a roadsurface in the fourth and fifth embodiments. FIG. 23B shows arelationship between a piston speed of a shock absorber and a vehiclespeed. FIG. 23C shows timing charts corresponding to FIG. 23A. FIGS.24A, 24B, 24C and 24D .[.shows.]. .Iadd.show .Iaddend.flowcharts ofprocess steps executed by the ECU in the fourth embodiment.

FIG. 25 shows a timing chart explaining a vehicle height data samplingtime interval t and a vehicle height judgment time interval ts.

FIG. 26 shows a relationship between reference values h1 and h2 and thevehicle speed V.

FIG. 27A shows a schematic figure of a vehicle passing a dip of a roadsurface in the fourth embodiment. FIG. 27B shows timing chartscorresponding to FIG. 27A.

FIGS. 28A, 28B, 28C and 28D show flowcharts of process steps executed bythe ECU in the fifth embodiment.

FIG. 29A shows a schematic figure of a vehicle passing a dip of a roadsurface in the fifth embodiment. FIG. 29B shows timing chartscorresponding to FIG. 29A.

FIG. 30 shows a relationship between the vehicle height change judgmenttime ts and the vehicle speed V. FIGS. 31A and 31B .[.shows.]..Iadd.show .Iaddend.sectional views of a variable-stiffness bush used ina suspension characteristic alteration means.

FIGS. 32A and 32B show sectional views of another variable-stiffnessbush.

FIGS. 33A, 33B, 33C, 33D, 33E, 33F and 33G show constructions of avariable-stiffness stabilizer.

FIGS. 34A and 34B show constructions of another variable-stiffnessstabilizer.

FIGS. 35A, 35B and 35C show constructions of still anothervariable-stiffness stabilizer.

FIGS. 36A and 36B show constructions of a unit for coupling avariable-stiffness stabilizer and a lower control arm to each other.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an outline of the first and second embodiments of thepresent invention. In these embodiments, the distance between a body aof an automobile and its front wheel d is found out by a front vehicleheight detection means e to generate a front vehicle height signal andsend it to a height data calculation means f.

The height data calculation means f calculates a plurality of secondarydata from the vehicle height signal and sends them to a judgment meansg, which sends a judgment result signal to the rear suspensioncharacteristic alteration means h. The rear suspension characteristicalteration means h alters a characteristic of rear suspensions cprovided between the body a and rear wheels b.

FIG. 2A shows a schematic figure of a vehicle j passing a small bump 1and a subsequent large bump m of a road surface k with a vehicle speedV. FIG. 2B shows timing charts of a front vehicle height and a rearvehicle height.

Provided a vehicle j is running on a road surface k and the front wheeld passes the small bump 1 and subsequently the large bump m as in FIG.2A, a change in front vehicle height is detected by the front vehicleheight detector e, which sends a front vehicle height signal as shown inFIG. 2B to the height data calculation means f. The height datacalculation means f calculates and generates a plurality of height dataas secondary data from the primary data of the front vehicle heightsignal. For example, a change in the front vehicle height signal hduring a short time interval ts is generated and sent to the judgmentmeans g. The judgment means g judges that the data exceeds acorresponding reference value and sends a command to the rear suspensioncharacteristic alteration means h to alter the rear suspensioncharacteristic to a `SOFT` state. This enables rear suspensions absorbthe shock that the rear wheels b receive in passing the small bump 1. Atthe same time, the height data calculation means f also calculates andgenerates, for example, a change in the front vehicle height signal Hduring a long time interval T and sends it to the judgment means g. Thejudgment means g judges that it exceeds another corresponding referencevalue and commands the rear suspension characteristic alteration means hto alter the rear suspension characteristic to a `HARD` state. Thistime, the alteration prevents large vibrations which may otherwise occurafter the rear wheels pass the large bump m.

FIG. 3 shows detail construction of the first embodiment of anautomobile having air suspensions which includes a rear suspensioncontroller according to the present invention.

A right front wheel vehicle height sensor 1 is provided between the bodyand right front wheel of the automobile to detect the distance betweenthe automobile body and a right suspension arm, which follows the motionof the wheel. A left front wheel vehicle height sensor 2 is providedbetween the body and left front wheel of the vehicle to detect thedistance between the vehicle body and a left suspension arm. The shortcylindrical bodies 1a and 2a of the vehicle height sensors 1 and 2 aresecured on the vehicle body. Links 1b and 2b extend from the centershafts of the bodies 1a and 2a almost perpendicularly to the centershafts. Turnbuckles 1c and 2c are rotatably coupled to the ends of thelinks 1b and 2b opposite the bodies 1a and 2a. The ends of theturnbuckles 1c and 2c opposite the links are rotatably coupled toportions of the suspension arms. A potentiometer, whose electricresistance changes depending on the rotation of the center shaft of thebody of each vehicle height sensor to take out the change in the vehicleheight in the form of a voltage change, is built in each of the bodiesof the vehicle height sensors 1 and 2. Although the vehicle heightsensors of the above-mentioned type are used in this embodiment, vehicleheight sensors of such other type may be used that plural lightinterrupters are provided in the body of each sensor, and a disk havinga slit coaxial with the center shaft of the sensor turns on or off thelight interrupters depending on the change in the vehicle height todetect the height. FIG. 3 also shows an air suspension 3 which isprovided between the suspension arm (not shown in the drawings) for theright rear wheel of the vehicle and the body thereof and extends inparallel with a suspension spring (not shown in the drawings). The airsuspension 3 includes a shock absorber 3a, a main air chamber 3b, anauxiliary air chamber 3c and an actuator 3d in the main, and has aspring function, a vehicle height adjustment function and a shockabsorber function. The same air suspensions 4, 5 and 6 are provided forthe left rear wheel, right front wheel and left front wheel of thevehicle, respectively.

FIG. 4 and FIG. 5 show constructions of the main part of the airsuspension 3. FIG. 5 shows a sectional view along a line V--V shown inFIG. 4. The other air suspensions 4,5 and 6 have the same constructionas the suspension 3. The air suspension 3 includes a conventional shockabsorber 3a composed of a piston and a cylinder, and an air spring unit14 provided in conjunction with the shock absorber. An axle (not shownin the drawings) is supported at the lower end of the cylinder 12a ofthe shock absorber 3a. An elastic cylindrical assembly 18 forelastically supporting a piston rod 12b to the vehicle body 16 isprovided at the upper end of the piston rod 12b extending from thepiston (not shown in the drawings) slidably fitted in the cylinder 12a.The shock absorber 3a is a conventional buffer whose damping force canbe varied for adjustment by operating the valve function of the piston.A control rod 20 for adjusting the damping force is liquid-tightly androtatably fitted with a sealing member 22 in the piston rod 12b.

The air spring unit 14 has a chamber 32 which is defined by acircumferential member 26 comprising a bottom 26a provided with anopening 24, through which the piston rod 12b is allowed to extend, and awall 26b rising from the peripheral portion of the bottom 26a, an upperhousing member 28a covering the circumferential member 26 and secured onthe vehicle body, a lower housing member 28b open at the lower end andcoupled to the lower end of the upper housing member 28a, and adiaphragm 30 made of an elastic material and closing the lower end ofthe lower housing member 28b. The chamber 32 is divided into a lowermain air chamber 3b and an upper auxiliary air chamber 3c by a partitionmember 36 secured on the bottom 26a of the circumferential member 26 andhaving an opening 34 corresponding to the opening 24 provided in thebottom 26a. Both the chambers 3b and 3c are filled with compressed air.The partition member 36 is fitted with a conventional buffer rubber 40which can be brought into contact with upper end of the cylinder 12a.The buffer rubber 40 has a passage 42 for connecting the openings 24 and34 to the main air chamber 3b.

The elastic cylindrical assembly 18 is disposed inside thecircumferential member 26 whose wall 26b defines the insidecircumferential surface of the auxiliary air chamber 3c, in such mannerthat the assembly 18 surrounds the piston rod 12b. The cylindricalelastic assembly 18 is provided with a valve unit 44 for controlling thecommunication of both the air chambers 3b and 3c. The assembly 18includes an outer cylinder 18a, a cylindrical elastic member 18b and aninner cylinder 18c which are disposed concentrically to each other. Thecylindrical elastic member 18b is secured on both the cylinders 18a and18b. The outer cylinder 18a of the assembly 18 is press-fitted on thewall 26b of the circumferential member 26 secured on the vehicle body,under the action of the upper housing member 28a. The valve casing 44aof the valve unit 44, through which the piston rod 12b is allowed toextend, is secured on the inner cylinder 18c. Since the piston rod 12bis secured on the valve casing 44a, the piston rod is elasticallysupported to the vehicle body by the cylindrical elastic assembly 18. Anannular air sealing member 46 is tightly packed in between the outercylinder 18a and the bottom 26b of the member 26. An annular air sealingmember 48 is tightly packed in between the piston rod 12b and the valvecasing 44a. An annular air sealing member 50 is tightly packed inbetween the inner cylinder 18c and the valve casing 44a.

The valve casing 44a has a hole 52 which is open at both the ends andextends in parallel with the piston rod 12b. A rotary valve 44b isrotatably supported in the hole 52. The valve 44b includes a mainportion 56a, which can be brought into contact with a lower positioningring 54a provided at the lower end of the hole 52, and a small-diameteroperating portion 56b projecting from the main portion above the elasticcylindrical assembly 18. An upper positioning ring 54b, which cooperateswith the lower positioning ring 54a to prevent the valve 44b fromdropping out of the hole 52, is provided at the upper end of the hole52. An annular sealing base 60 holding an inner air sealing member 58aand an outer air sealing member 58b for tightly closing the hole 52 isprovided between the upper positioning ring 54b and the main portion 56aof the valve 44b. A friction reducer 62 for smoothing the rotativemotion of the valve 44b when the main portion 56a of the valve is pushedto the sealing base 60 by air pressure is provided between the sealingbase and the main portion of the valve.

A chamber 64, which connects with the main air chamber 3b through theopenings 24 and 34 and the passage 42 of the buffer rubber 40, is formedin the lower portion of the elastic cylindrical assembly 18. The mainportion 56a of the valve 44b has a recess 66 open to the chamber 64, andhas a communication passage 68 extending through the main portion 56a ina diametral direction thereof across the recess 66.

The valve casting 44a, which houses the valve 44b, has a pair of airpassages 70, each of which can connect at one end with the communicationpassage 68, as shown in FIG. 5.

The air passages 70 extend on almost the same plane outwards in adiametral direction of the hole 52, toward the peripheral surface of thevalve 44b. The other end of each air passage 70 is open to theperipheral surface of the valve casing 44a through a face hole 72. Anair passage 74, which can connect at one end with the communicationpassage 68, extends on almost the same place as the pair of air passages70 toward the peripheral surface of the valve .[.casting.]. .Iadd.casing.Iaddend.44a, between the pair of air passages 70 outside the hole 52.The diameter of the air passage 74 is smaller than that of each of theair passages 70. The other end of the air passage 74 is open to theperipheral surface of the valve casing 44a through a face hole 75. Theinside circumferential surface of the inner cylinder 18c covering theperipheral surface of the valve casing 44a has an annular recess 76which surrounds the peripheral surface of the valve casing to connectthe face holes 72 and 75 for the air passages 70 and 74 to each other.

The inner cylinder 18c has an opening 78 which extends continuously tothe recess 76 which constitutes an annular air passage. The cylindricalelastic member 18b has through holes 80, which extend outwards in theradial direction of the member 18b corresponding to the openings 78. Thethrough holes 80 are made open to the peripheral surface of the outercylinder 18a through the openings 82 of the cylinder so that theopenings 78 and 82 and the through holes 80 define an air passageincluding the air passages 70 and extending through the elasticcylindrical assembly 18.

The peripheral surface of the wall 26b of the circumferential member 26covering the outer cylinder 18a are provided with plural openings 84which are located at equal intervals in the circumferential direction ofthe member 26 and extend continuously to the auxiliary air chamber 3c toconnect the openings 78 and 82 and the through holes 80 to the auxiliaryair chamber 3c. The peripheral surface of the outer cylinder 18a isprovided with an annular recess 86 which surrounds the outer cylinder atthe openings 82 to connect the openings 84, 78 and 82 and the throughholes 80 to each other. The openings 84 extend continuously to therecess 86 constituting an annular air passage.

Although the openings 78 and 82 and the through holes 80 are providedcorrespondingly to the two air passages 70 of the valve casing 44a inthe embodiment shown in FIG. 3(B), the air passages 70 and 74 can beprovided in optional positions in the circumferential direction of theelastic member 18b because the annular air passage 76, with which theair passages 70 and 74 connect, is formed between the inner cylinder 18cand the valve casing 44a.

A control rod 20 for adjusting the damping force of the shock absorber3a, and a conventional actuator 3d for rotating the valve 44b of thevalve unit 44, are provided at the upper end of the piston rod 12b, asshown FIG. 4.

Since the air suspension 3 has the above-mentioned construction, the airsuspension performs actions described hereinafter. When the valve 44b iskept in such a closed position shown in FIG. 5 that the communicationpassage 68 of the valve does not connect with any of the air passages 70and 74 of the valve casing 44a, the main air chamber 3b and theauxiliary air chamber 3c are disconnected from each other so that thespring constant of the suspension 3 is set at a large value. When theactuator 3d has rotated the valve 44b into such a position that thecommunication passage 68 of the valve connects with the large-diameterair passages 70 of the valve casing 44a, the main air chamber 3b isconnected to the auxiliary air chamber 3c through the communicationpassage 68 communicating with the main air chamber, the large-diameterair passages 70 and the openings 78 and through holes 80 of the elasticassembly 18 and the openings 82 and 84, so that the spring constant ofthe suspension 3 is set at a small value. When the valve 44b is rotatedinto such a position by the regulated actuator 3d that the communicationpassage 68 of the valve connects with the small-diameter communicationpassage 74 of the valve casing 44a, the main air chamber 3b is connectedto the auxiliary air chamber 3c through the communication passage 68communicating with the main air chamber, the small-diameter air passage74, the air passage 76, the openings 78 and through holes 80 of theelastic assembly 18 and the openings 82 and 84, so that the springconstant of the suspension 3 is set at an intermediate value because thesmall-diameter air passage 74 provides a higher air flow resistance thanthe large-diameter air passages 70.

Leveling valves 151 through 154 are provided for the air suspensions 3through 6, respectively, as shown in FIG. 3. A compressed air feed anddischarge system 200, which is described below, is connected to ordisconnected from the main air chambers 3b through 6b of the airsuspensions 3 6 by the leveling valves 151 through 154 depending onwhether electricity is supplied to solenoids 151a through 154a or not.When the leveling valves 151 through 154 are opened, compressed air isfed to the air suspensions, the height of the vehicle is increased. Ifthe compressed air is discharged from the air suspensions, the height ofthe vehicle is decreased. When the leveling valve 151 through 154 areclosed, the height of the vehicle is maintained.

In the compressed air feed and discharge system 200, a compressor 200bis driven by a motor 200a to produce the compressed air. An air drier200c dries the compressed air to be fed to the air suspensions 3 through6, to protect pipes and the parts of the air suspensions from moisturephase change in the main air chambers 3b through 6b and auxiliary airchambers 3c through 6c of the air suspensions. When the compressed airis fed to the air suspensions, a check valve 200d provided with a fixedorifice is opened. When the compressed air is discharged from the airsuspensions, the check valve 200d is closed so that the air flows outthrough only the fixed orifice. When the compressed air is dischargedfrom the air suspensions 3 through 6, a releasing solenoid valve 200e isdriven so that the compressed air discharged from the air suspensionsthrough the fixed orifice at the check valve 200d and through the airdrier 200c is released into the atmosphere. The solenoid valve 200e canbe regulated to change the volume of each of the main air chambers ofthe air suspensions 3 through 6 to adjust the height of the vehicle.

A vehicle speed sensor 250 is provided in a speedometer, for example, sothat the sensor sends out a pulse signal corresponding to the speed ofthe vehicle, in response to the motion of the axle of the vehicle.

The output signals of the vehicle height sensors 1 and 2 and the vehiclespeed sensor 250 are entered into an electronic control unit(hereinafter referred to as ECU) 300, which processes these signals tosend out drive signals to the actuators 3d through 6d of the airsuspensions 3 through 6, the leveling valves 151 through 154, the motor200a of the compressed air feed and discharge system 200 and thesolenoid valve 200e to perform appropriate control if necessary. FIG. 6shows the construction of the ECU 300. A central processing unit(hereinafter referred to as CPU) 301 receives the output data from thesensors and performs operations on the data, in response to a controlprogram, to carry out process steps for the control of various units ormean or the like. The control program and initial data are stored in aread-only memory (hereinafter referred to as ROM) 302. The data, whichare entered in the ECU 300, and data necessary for operations andcontrol, are stored into and read .[.our.]. .Iadd.out .Iaddend.of arandom-access memory (hereinafter referred to as RAM) 303. A backuprandom-access memory (hereinafter referred to as backup RAM) 304 isbacked up by a battery so that even if the ignition key switch of theautomobile is turned off, the backup RAM retains data which are neededafter the turning-off of the switch. An input section 305 includes aninput port not shown in the drawings, a waveshaping circuit provided ifnecessary, a multiplexer which selectively sends out the output signalsof the sensors to the CPU 301, and an A/D converter which changes ananalog signal into a digital signal. An output section 306 includes anoutput port not shown in the drawings, and a drive circuit for drivingthe actuators according to the control signals of the CPU 301 asoccasion demands. A bus 307 connects circuit components such as the CPU301 and the ROM 302, the input section 305 and the output section 306 toeach other to transmit data. A clock circuit 308 sends out a clocksignal at prescribed intervals to the CPU 301, the ROM 302, the RAM 303and so forth so that a control timing is set by the clock signal.

If the output signal of the vehicle height sensor 1 is a digital signal,the signal is transmitted to the CPU 301 through the input section 305including a buffer as shown in FIG. 7. If the output signal of thevehicle height sensor 1 is an analog signal, a construction as shown inFIG. 8 is provided. In the latter case, the vehicle height sensor 1sends out the analog signal of a voltage corresponding to the height ofthe vehicle. The analog voltage signal is converted into a voltageVHF(CR) indicating an average height of the vehicle, by a CR filtercircuit 305a made of a low-pass filter. The voltage VHF(CR) is appliedto an A/D converter 305b. The analog voltage signal is also directlyapplied as a voltage VHF(S) indicating the current height of thevehicle, to the A/D converter 305b. The converter 305b changes both theinput signals into digital signals through the action of a multiplexer.The digital signals are transmitted from the converter to the CPU 301.The same applies to the left front wheel vehicle height sensor 2.

Here, relationships between the first and second judgment conditions andvarious variables of the first embodiment are explained with FIG. 9. Ashort time interval t in FIG. 9 is for sampling outputs from the frontvehicle height sensors H1R and H2L and a time interval ts is for takingup a height data for judging in the first judgment condition. There is arelationship

    ts=t×n1

between them, where n1 is an integer. For the first judgment condition,the largest front vehicle height change h is calculated by

    h=VHh-VHl.

where VHh and VHl denote a maximum front vehicle height and a minimumfront vehicle height respectively during a time interval ts. When theheight change h exceeded the corresponding reference value h1 in thefirst judgment condition, the rear suspension characteristic is alteredfrom a `SPORT` state which has been selected for a normal cruising ofthe automobile to a `SOFT` state. A time interval tr is for taking up aheight data for judging to return the altered rear suspensioncharacteristic in the first judgment condition. There is a relationshiptr=t×n3, where n3 is an integer. The largest front vehicle height changehr during a time interval tr is calculated by hr=VHh-VHl. When theheight change hr is smaller than the corresponding reference value h1 inthe first judgement condition, the rear suspension characteristic isreturned to the `SPORT` state fron the `SOFT` state. The intervals tsand tr may be the same, i.e. ts=tr. The reference value for alterationh1 and the reference value for returning h2 are determined as h1>h2. Atime interval T is for taking up a height data for the second judgmentcondition. There is a relationship T=t×n2, where n2 is an integer. Forthe second judgment condition, the largest front vehicle height change His calculataed by H=VHH-VHL, where VHH and VHL denote a maximum and aminimum front vehicle heights respectively during a time interval T.When the height change H exceeds the corresponding reference value H1 inthe second judgment condition, the rear suspension characteristic isaltered from a `SOFT` or `SPORT` state to a `HARD` state. A timeinterval Tr is for taking up a height data for judging to return thealtered rear suspension characteristic in the second judgment condition.There is a relationship

    Tr=T×n4,

where n4 is an integer. The largest front vehicle height change Hrduring a time interval Tr is calculated by

    Hr=VHH-VHL.

When the height change Hr is smaller than the corresponding referencevalue H2 in the second judgment condition, the rear suspensioncharacteristic is returned to the `SOFT` or `SPORT` state from the`HARD` state. The time intervals .[.Ts.]. .Iadd.T .Iaddend.and Tr may bethe same, i.e., .[.Ts.]. .Iadd.T.Iaddend.=Tr. .[.the.]. .Iadd.The.Iaddend.reference value for alteration H1 and the reference value forreturning H2 are determined as

    H1>H2.

The process steps, which are performed by the ECU 300, are hereinafterdescribed referring to flow charts shown in FIGS. 10A-10E. Theflowcharts indicate the process steps performed by the ECU 300 inresponse to the vehicle height sensor 1 of the linear type which sendsout an analog signal, as shown in FIG. 8.

An outline of the process steps shown in the flow charts is described asfollows with step numbers in the parentheses:

(1) A current front vehicle height VH(S)n is detected (108);

(2) The maximum front vehicle height and the minimum front vehicleheight corresponding to each judgement condition and a delay time forreturning rear suspension characteristic are calculated (110);

(3) It is judged whether the largest front vehicle height change exceedsa corresponding reference value h1 in the first judgment condition(122);

(4) If the largest front vehicle height change exceeds the referencevalue h1, the rear suspension characteristic is altered (160);

(5) Another front vehicle height is detected, the process steps asdescribed above are repeated (104-116) and it is judged whether time haselapsed for returning the altered rear suspension characteristic (126);

(6) After the time had elapsed, it is judged whether the largest frontvehicle height change is smaller than a corresponding reference value h2in the first judgment condition (132);

(7) If the largest front vehicle height change is smaller than thereference value h2, the rear suspension characteristic is returned tothe original state (160);

(8) If the largest front vehicle height change does not exceed thereference value h1 in the first judgment condition (122), it is thenjudged whether the largest front vehicle height change exceeds anothercorresponding reference value H1 (144);

(9) If the largest front vehicle height change exceeds the referencevalue H1, the rear suspension characteristic is altered (160);

(10) Another front vehicle height is detected, the process steps asdescribed before are repeated (104-118, 138) and it is judged whethertime has elapsed for returning the altered rear suspensioncharacteristic (150);

(11) After the time elapsed, it is judged whether the largest frontvehicle height change is smaller than a corresponding reference value H2in the second judgment condition (156); and

(12) If the largest front vehicle height change is smaller than thereference value H2, the rear suspension characteristic is returned tothe original state (160).

Among the process steps as described in (1)-(12), those relating to theeffects of the present invention are (1)-(4), (8) and (9), while those(5)-(7) and (10)-(12) are supplementary process steps for thisembodiment.

The alteration of rear suspension characteristic means, if the drivingcondition is that requires especially preventing shocks at the rearpassanger seat, alteration to a `SOFT` state. The actuators 3d and 4dare driven to connect the main air chambers 3b and 4b and the auxiliaryair chambers 3c and 4c, respectively, or the damping forces of the shockabsorbers 3a and 4a are decreased. If, on the other hand, the drivingcondition is that the controllability and stability are required againstlarge vibrations due to the road surface irregularities, the alterationof the suspension characteristic means the alteration to a `HARD` state.The main air chambers 3b and 4b and the auxiliary air chambers 3c and 4care disconnected to make the spring constant of the air suspensions highor the damping forces of the shock absorbers 3a and 4a are increased.And if the driving condition is that for a normal cruising, the rearsuspension characteristic is kept to be a `SPORT` state, which is anintermediate state between the `SOFT` state and the `HARD` state..[.In.]. .Iadd.The .Iaddend.spring constant of the rear air suspensionsor the damping forces of the shock absorbers are set to be anintermediate value.

The details of the process steps are hereinafter described. The processsteps are repeatedly performed in every 5 msec. It is first judgedwhether or not the process steps are being performed for the first timesince the activation of the ECU 300 (100). If the process steps arejudged to be being performed for the first time, initial setting iseffected (102), all variables are cleared and all flags are reset. Afterthe initial setting is effected or if the process steps in the routineare judged to be performed for the second time or later, it is judgedwhether a timer T1 exceeds a front vehicle height sampling time intervalt (104). The timer T1 is counted at step 200 in the intermittentinterrupt routine process steps of FIG. 10(E). When the timer T1 elapsesthe time interval t, the timer T1 is reset (106) and current frontvehicle height VH(S)n is inputted from the front vehicle height sensors1 and 2 (108).

To detect the current vehicle height, either of the outputs of thevehicle height sensors for the right and left front wheels of thevehicle may be used. Since rear wheels receives a shock whichever of thefront wheels has moved up or down due to the bump or dip of the roadsurface, the average of the outputs of both the vehicle height sensorsfor the front wheels may be used or the larger one of the outputs may beused.

Then, a delay time Tk for returning the rear suspension characteristic,the maximum front vehicle height for the first judgment condition VHh,the minimum front vehicle height for the first judgment condition.[.VH1.]. .Iadd.VHl.Iaddend., the maximum front vehicle height for thesecond judgment condition VHH and the minimum front vehicle height forthe second judgment condition VHL are calculated (110). Details of thisstep 110 is explained with FIG. 10C as follows.

First, it is judged whether the current front vehicle height VH(S)nexceeds the past maximum front vehicle height VHh for the firstjudgement condition (110a). If the result is `YES`, a new maximum frontvehicle height VHh is determined to be the current front vehicle heightVH(S)n (110b). Otherwise it is judged whether the current front vehicleheight VH(S)n is less than the past minimum front vehicle height.[.VH1.]. .Iadd.VHl .Iaddend.for the first judgment condition (110c). Ifthe result is YES, a new minimum front vehicle height .[.VH1.]..Iadd.VHl .Iaddend.is determined to be the current front vehicle heightVH(S)n (110d). Otherwise, it is judged whether the current front vehicleheight VH(S)n exceeds the past maximum front vehicle height VHH for thesecond judgment condition (110e). If the result is YES, a new maximumfront vehicle height VHH is determined to be the current front vehicleheight VH(S)n (110f). Otherwise it is judged whether the current frontvehicle height VH(S)n is less than the past minimum front vehicle heightVHL for the second judgement condition (110g). If the result is YES, anew minimum front vehicle height VHL is determined to be the currentfront vehicle height VH(S)n (110h). Otherwise the vehicle speed isdetected by the vehicle speed sensor 250 (100i) and the delay time Tk iscalculated (110j) as

    Tk=WB/V+A1,

where WB is a wheelbase of the vehicle, V is a vehicle speed and A1 is acompensatory term regarding of a detecting lag and passing time. Thoseare details of step 110.

Returning to FIG. 10A, it is judged whether `AUTO` mode is selected bythe driver (112). If the `AUTO` is selected, the vehicle speed iscompared with a reference value V0(114).

If V>=V0 the vehicle is judged to be moving and subsequent process stepsare executed.

If is judged whether a flag F1 is set (116), which indicates the processstep is in the first judgement condition. This time, as F1=0, step 118is selected and it is judged whether a time T2 exceeds a time intervalts for alteration control of the first judgement condition. The timer T2is counted at step 200 in the intermittent interrupt routine processsteps of FIG. 10E. When the timer T2 elapses the time interval ts, thetimer T2 is reset (120).

Then it is judged whether the largest front vehicle height change duringthe time interval ts exceeds a corresponding reference value h1 foralteration control of the first judgment condition (122). If the resultis `YES`, the flat F1 is set (124) and the process step goes to step136. Otherwise, the process step directly goes to step 136, and themaximum front vehicle height VHh and the minimum front vehicle height.[.VH1.]. .Iadd.VHl .Iaddend.during the time interval ts are replaced bythe current front vehicle height VH(S)n.

Then at step 138 in FIG. 10B, it is judged whether a flat FA is set,which indicates the process step is in the second judgment condition.This time, as FA=0, step 140 is selected and it is judged whether atimer T4 exceeds a time interval T for alteration control of the firstjudgement condition. The timer T4 is counted at step 200 in theintermittent interrupt routine process steps of FIG. 10E. This time, asT4 does not exceed the time interval T, the process step goes to step160, where the rear suspension characteristic alteration actuators aredriven. Details of the step 160 are explained with FIG. 10D as follows.

It is judged whether the flag F1 is set (160a) and, since this timeF1=1, it is judged whether the flag FA is set (160c). Since FA=0 thistime, it is judged whether a flat FSF is set (160f). Since this timeFSF=0, the rear suspension characteristic is altered to the `SOFT`state, the flag FSF is set and flags FSP and FH representing the `SPORT`and `HARD` states respectively are reset (160i). Then a timer T3 forcounting a delay time until returning the rear suspension characteristicis reset (160j). Those are details of step 160 and the process stepsreturns to B in FIG. 10B.

After executing steps 100-114, step 126 is selected at step 116, sinceF1=1 this time. It is judged whether the timer T3 exceeds a delay timeTk for returning the rear suspension characteristic (126). The timer T3is counted at step 200 the intermittent interrupt routine process stepsof FIG. 10E. If the result is `NO`, process steps goes to step 138 and,since FA=0 this time, then the step 140, where it is judged whether thetimer T4 exceeds the time interval T. If the timer T4 exceeds the timeinterval T, the timer T4 is reset (142). Then it is judged whether thelargest front vehicle height change during the time interval T exceeds acorresponding reference value H1 for alteration control of the secondjudgment condition (144).

If the result is YES, the flag FA is set (146), and the process stepsgoes to step 148.

This time, the explanation is proceeded as the result is NO, so that theprocess step directly goes to step 148, and the maximum front vehicleheight VHH and minimum front vehicle VHL during the time interval T arereplaced by the current vehicle height VH(S)n. Then step 160 isexecuted, whose details are explained with FIG. 10D as follows. Sincecurrent flags are such that F1=1, FA=0 and FSF=1, the process stepsproceed through steps 160a, 160c and 160f and go back to B in FIG. 10A.Then after executing 100 and 104-.[.106.]. .Iadd.116 .Iaddend.and whenthe timer T3 exceeds Tk (126), it is judged whether the timer T2 exceedsa time interval tr for returning control of the first judgmentcondition. The timer T2 is counted at step 200 in the intermittentinterrupt routine process steps of FIG. 10E. .[.when.]. .Iadd.When.Iaddend.the timer T2 elapsed the time interval tr, the timer T2 isreset (130).

Then, it is judged whether the largest front vehicle height changeduring the time interval tr is less than a corresponding reference valueh2 for returning control of the first judgement condition (132). If theresult is YES, the flag F1 is reset (134) and the process step goes tostep 136. This time, the explanation is proceeded as the result is`YES`, so that the maximum front vehicle height VHh and minimum frontvehicle height VHl during the time interval tr are replaced by thecurrent front vehicle height .[.(.].VH(S)n. Then, the process stepsproceed through steps 138, 140 and 160, whose details are explained withFIG. 10D as follows. Since current flags are such that F1=0, FA=0,FSF=1, FH=0 and FSP=0, the process steps proceed through 160a, 160b,160e and 160h, where the rear suspension characteristic is altered fromthe `SOFT` state to the `SPORT` state, the flag FSP is set and the flagsFH and FSF are reset. Lastly for the process steps of step 160, thetimer T3 is reset at step 160j.

As another cycle of the routine from B of FIG. 10A, steps 100 and104-116 are performed. Since this time F1=0, the process steps proceedthrough steps 118, 120, and 122, where the result this time is providedto be NO. The process step proceed through steps 138, 140 and 142, and140 of FIG. 10B, where it is judged whether the largest front vehicleheight change during the time interval T exceeds a correspondingreference value H1 for alteration control of the second judgmentcondition (144). Provided the result is YES, the flag FA is set (146),and the process step goes to step 148. Since current flags are such thatF1=0, FA=1, FSP=1, FH=0 and FSF=0, the process step proceed through160a, 160b, 160d and 160g, where the rear suspension characteristic isaltered from the `SPORT` state to the `HARD` state, the flage FH is setand the flags FSP and .[.FSf.]. .Iadd.FSF .Iaddend.are reset. Lastly forthe process steps of step 160, the timer T3 is reset at step 160j.

As another cycle of the routine from B of FIG. 10A, steps 100 and104-116 are performed. Since this time F1=0, the process steps proceedthrough steps 118, 120, 122, 136 and 138 of FIG. 10B. As FA=1 this time,it is judged whether the timer T3 exceeds a delay time Tk for returningthe rear suspension characteristic (150). The timer T3 is counted atstep 200 in the intermittent interrupt routine process steps of FIG.10E. If the result is NO, the process step goes to step 160 and, sincecurrent flags are such that F1=1, FA=1, FH=1, FSP=0 and FSF=0, theprocess steps proceed through steps 160a, 160b and 160d and go back to Bin FIG. 10A.

As described before, the process steps proceed through 100, 104-116,118, 120, 122 and 136 of FIG. 10A then 138 and 150 of FIG. 10B. Afterthe time interval Tk, it is judged whether the timer T4 exceeds a timeinterval Tr for returning control of the second judgment condition(152). .[.the.]. .Iadd.The .Iaddend.timer T4 is counted at step 200 inthe intermittent interrupt routine process steps of FIG. 10E. When thetimer T4 elapses the time interval Tr, the timer T4 is reset (154).

Then it is judged whether the largest front vehicle height change duringthe time interval Tr is less than a corresponding reference value H2 forreturning control of the first judgment condition (156). If the resultis YES, the flag FA is reset (158), and the process steps goes to step148.

Then at step 160, since current flags are such that F1=0, FA=0, FSP=0,FH=1 and FSF=0, the process steps proceed through 160a, 160b, 160e, and160h, where the rear suspension characteristic is altered from the`HARD` state to the `SPORT` state, the flag FSP is set and the flags FHand FSF are reset. Lastly for the process steps of step 160, the timerT3 is reset at step 160j. Then other routine cycles are repeated from Bof FIG. 10A.

In the explanation above, the order of the alteration of the rearsuspension characteristic is such that alteration by the first judgmentcondition, returning by the first judgment condition, alteration by thesecond judgment condition and then returning by the second judgmentcondition. In actual driving case, though, the order is not necessarilythe same as that. For example, if a large bump .[.is followed by.]..Iadd.follows .Iaddend.a small bump, the rear suspension characteristicis altered to the `HARD` state by the second judgment conditionimmediately after passing a small bump with the `SOFT` state, and thenreturned to the `SPORT` state by the second judgment condition after thevibration decays.

The process steps in FIG. 10D (160a, 160b, 160c) are so arranged thatthe second judgment condition is given a priority over the firstjudgment condition. This is for improving the controllability andstability of the automobile in case sporadic small irregularities arefollowed by large irregularities of the road surface.

An example of control timing performed by the first judgment conditionis then explained with FIGS. 11A and 11B. FIG. 11A shows an automobile jwhose front wheel W1R or W1L is passing a small dip O of a road surfacek with a speed V. FIG. 11B shows time charts of the output of the frontvehicle height sensor 1 or 2, the drive signal for the rear suspensioncharacteristic alteration actuators 3d and 4d, the rear suspensioncharacteristic and the rear vehicle height.

The front wheel W1R or W1L begins to move down into the small dip O at atime point t1. Since then the output VH(S)n of the front vehicle heightsensor 1 or 2 becomes large. From the time point t1, the front vehicleheight is sampled every time interval t as shown in FIG. 9, and at atime point t2, which is a time interval ts later than the time point t1,the ECU 300 judges that the largest front vehicle height change hexceeds a corresponding reference value h1. At this time point, the ECU300 drives the rear suspension alteration actuators 3d and 4d to alterthe rear suspension characteristic to a `SOFT` state, i.e. the main airchambers 3b and 4b are connected with the auxiliary air chambers 3c and4c, respectively, by the large section passage 70. The alterationoperation is finished at a time point t3, a time interval Ta later thant2. The driving signal from the ECU 300 is sent to the actuators 3d and4d until a time point t4, though the alteration operation per se isfinished before at the time point t3. Between the time point t1 and atime point t5, which is a time interval Tc later than the time point t1,the rear wheels W2R, W2L begin to move down into the small dip O.

At a time point t6, which is a time interval Tk for returning controlafter the time point t2, the rear wheels W2R, W2L have passed the smalldip O. At a time point t7, which is a time interval tr later than thetime point t6, the ECU 300 judges that the largest front vehicle heightchange hr is less than a corresponding reference value h2. At this timepoint, the ECU 300 drives the rear suspension alteration actuators 3dand 4d to alter the rear suspension characteristic to a `SPORT` state,i.e. the main air chambers 3b and 4b are connected with the auxiliaryair chambers 3c and 4c, respectively, by the small section passage 74.

The alteration operation is finished at a time point t8, a time interval.[.ta.]. .Iadd.Ta .Iaddend.later than .[.T7.]. .Iadd.t7.Iaddend.. Thedriving signal from the ECU is sent to the actuators 3d and 4d until atime point t9, though the alteration operation per se is finished beforeat the time point t8.

Another example of control timings performed by the second judgmentcondition is then explained with FIGS. 12A and 12B. FIG. 12A shows anautomobile j whose front wheel W1R or W1L is passing a large dip P of aroad surface k with a speed V. FIG. 12B shows time charts of the outputof the front vehicle height sensor 1 or 2, the drive signal for the rearsuspension characteristic alteration actuators 3d and 4d, the rearsuspension characteristic and the rear vehicle height.

The front wheel W1R or W1L begins to move down into the large dip P at atime point .[.t12.]. .Iadd.t11.Iaddend.. Since then the output VH(S)n ofthe front vehicle height sensor 1 or 2 becomes large. From the timepoint t11, the front vehicle height is sampled every time interval t asshown in FIG. 9, and at a time point t12, which is a time interval Tlater than the time point t11, the ECU 300 judges that the largest frontvehicle height change H exceeds a corresponding reference value H1. Atthis time point, the ECU drives the rear suspension alteration actuators3d and 4d to alter the rear suspension characteristic to a `HARD` state,i.e. the main air chambers 3b and 4b are connected with the auxiliaryair chambers 3c, 4c, respectively. The alteration operation is finishedat a time point t13, a time interval Ta later than t12. The drivingsignal from the ECU 300 is sent to the actuators 3d and 4d until a timepoint t14, though the alteration operation per se is finished before thetime point t13. The alteration of the rear suspension characteristic tothe `HARD` state is either from a `SOFT` state or from a `SPORT` state.Between the time point t11 and a time point t15, which is a timeinterval Tc later than the time point t11, the rear wheels W2R, W2Lbegin to move down into the large dip P. Here the time interval Tc isthat for the front and rear wheels to pass the dip. So the time pointt13 should be preferably before the time point t15, but other cases maybe allowed, i.e. the time points t13 and t15 may coincide or the timepoint t13 may be a little later than the time point t15, since thisalteration is aimed to prevent a large vibrations.

At a time point t16, which is a time interval Tk for returning controlafter the time point t12, the rear wheels W2R, W2L have passed the largedip P. At a time point t17, which is a time interval Tr later than thetime point t16, the ECU 300 judges that the largest .[.from.]..Iadd.front .Iaddend.vehicle height change Hr is less than acorresponding reference value H2. At this time point, the ECU 300 drivesthe rear suspension alteration actuators 3d and 4d to alter the rearsuspension characteristic to a `SPORT`, i.e. the main air chambers 3band 4b are connected with the auxiliary air chambers 3c and 4c,respectively, by the small section passage 74, or the rear suspensionalteration actuators 3d and 4d are driven to alter the rear suspensioncharacteristic to a `SOFT` state, i.e. the main air chambers 3b and 4bare connected with the auxiliary air chambers 3c and 4c, respectively,by the large section passage 70.

Another example of control timing of a case of an automobile passing asmall bump O which is judged by the first judgment condition followed bya large bump P which is judged by the second judgment condition isexplained with FIGS. 13A and 13B. FIG. 13A shows an automobile j whosefront wheels W1R or W1L is passing a small dip O and a large dip P of aroad surface k with a speed V. FIG. 13B shows time charts of the outputof the front vehicle height sensor 1 or 2, the drive signal for the rearsuspension characteristic alteration actuators 3d and 4d, the rearsuspension characteristic and the rear vehicle height.

The front wheel W1R or W1L beings to move down into the small dip O at atime point t41. Since then, the output VH(S)n of the front vehicleheight sensor 1 or 2 becomes large. From the time point t41, the frontvehicle height is sampled every time interval t as shown in FIG. 9, andat a time point t42, which is a time interval ts later than the timepoint t41, the ECU 300 judges that the largest front vehicle heightchange h exceeds a corresponding reference value h1 by the firstjudgment condition. At this time point, the ECU 300 drives the rearsuspension alteration actuators 3d and 4d to alter the rear suspensioncharacteristic from a normal `SPORT` state to a `SOFT` state, i.e. themain air chambers 3b and 4b are connected with the auxiliary airchambers 3c and 4c, respectively, by the large section passage.

The alteration operation is finished at a time point t43, a timeinterval Ta later than t42. The driving signal from the ECU 300 is sentto the actuators 3d and 4d until a time point t44, though the alterationoperation per se is finished before the time point t43.

Then at a time point t46, which is a time interval T later than the timepoint t41, the ECU judges that the largest front vehicle height change Hduring the time interval T exceeds a corresponding reference value H1 bythe second judgment condition. At this time point t46, the ECU 300drives the rear suspension alteration actuators 3d and 4d to alter therear suspension characteristic from the `SOFT` state to a `HARD` state.The alteration operation is finished at a time point t48, a timeinterval Ta later than t46. The driving signal from the ECU 300 is sentto the actuators 3d and 4d until a time point t49, though the alterationoperation per se is finished before at the time point t48. So the rearwheels W2R and W2L pass the large bump P with the `HARD` statesuspension characteristic to prevent large vibration. At a time pointt50, which is a time interval Tr later than the time point t47, the ECU300 judges that the largest front vehicle height change Hr is less thana corresponding reference value H2. At this time point t50, the ECU 300drives the rear suspension alteration actuators 3d and 4d to alter therear suspension characteristic from the `HARD` state to the `SPORT`state.

The alteration operation is finished at a time point t51, a timeinterval Ta later than t50. The driving signal from the ECU 300 is sentto the actuators 3d and 4d until a time point t52, thourgh thealteration operation per se is finished before at the time point t51.

As described above, the first embodiment is so arranged that shocks areprevented at the rear part of the automobile and the ride comfortthereof is maintained in passing sporadic bumps or dips. And afterpassing them, the suspension characteristic is returned to fit to anormal road surface to maintain the controllability and stability. Inthe above embodiment, the rear suspension characteristic is altered to`SOFT`, `SPORT` and `HARD` states according to the judgment results, thealteration steps may be increased by so arranging the air suspensions orshock absorbers or combining the various characteristics of everycomponent.

The degree of freedom in designing the driving characteristic of anautomobile is increased. While the first embodiment uses two judgmentconditions, it is possible to adopt three or more judgment conditions tocope with various road surface irregularities.

As the first embodiment gives the second judgment condition a priorityover the first judgment condition, i.e. hardening the rear suspensioncharacteristic is given a priortity, the driving controllability andstability are most regarded. And since the first embodiment hasdifferent reference values for altering the rear suspensioncharacteristic and for returning it, hunting of the alteratio and returncontrol is eliminated.

The second embodiment of the present invention is then explained withflow charts of FIGS. 14A, 14B, 14C, 14D and 14E and timing charts ofFIGS. 15 and 16. The construction of the apparatus of this embodiment isthe same as that of the first embodiment, as FIGS. 3-8. The flow chartsof this embodiment are so made to coincide by the last two digits of thestep number with that of the first embodiments, as FIGS. 10A-10E, if thecorresponding steps are similar with each other.

The main difference between the first and the second embodiments lies inwhen to alter the rear suspension characteristic. While in the firstembodiment the alteration control is performed as soon as the frontvehicle height exceedes the corresponding reference value, it isperformed just before the rear wheels pass the bump or dip in thisembodiment. For that purpose, a delay time Td, which is a time intervalbetween the detection of the bump or dip by the front vehicle heightsensors and the beginning of the rear suspension characteristicalteration control, is introduced in the second embodiment.

The steps 300-308 in the flow chart of FIG. 14A are the same as thecounterparts of FIG. 10A of the first embodiment. At step 311, a delaytime Tk, the maximum front vehicle height VHh of the first judgmentcondition, the minimum front vehicle height .[.VH1.]. .Iadd.VHl.Iaddend.of the first judgment condition, the maximum front vehicleheight of the second judgment condition VHH and the minimum frontvehicle height of the second judgment condition VHL are calculated asthe first embodiment as well as the delay time Td. Details of the step311 is shown in FIG. 14C, where steps 311a-311j are the same as steps110a-110j of FIG. 10C. At step 311k, the delay time Td is calculated as

    Td=WB/V-A2-Ta,

where WB is a wheelbase, V is a vehicle speed, A2 is a compensatory termand Ta is a duration time of driving signal to the actuators to alterthe rear suspension characteristic.

Steps 312-336 of FIG. 14A and steps 338-358 of FIG. 14B are the same assteps 112-136 of FIG. 10A and steps 138-158 of FIG. 10B, respectively.Details of step 361, where the rear suspension characteristic is alteredafter a delay time Td, are hereinafter described with FIG. 14D. With astate for altering by the first judgment condition, i.e. the flags aresuch that F1=1, FA=0, FH=0, FSP=0 and FSF=0, the process steps proceedthrough steps 361a, 361c, 361f and 361i. At step 361i, the delay time Tdis put into a timer T5 and the flag FSF is set, where T5 is a timerwhich is counted down by an intermittent interrupt routine step 400 ofFIG. 14E. Timers T6 and T7 are also counted down by step 400. Since.[.T4.]. .Iadd.T5.Iaddend., T6, and T7 are all non-negative, the processsteps proceed through 361j, 361k, 361l and 361q. Since FH=0 at step361q, the value 2×Td is put into the timer T7. Since .[.FSO.]..Iadd.FSP.Iaddend.=0 at step 361s, 2×Td is put into the timer T6. Thensince FSF=1 (361u), the process steps of step 361 are finished and theprocess steps begin from B of FIG. 14A again. Though in these processsteps the timers T5, T6 and T7 are counted down (400), the timers T6 andT7 are renewed by a value 2×Td every time, preventing them from beingnegative. The timer T5, on the other hand is not renewed by theseroutines, so it becomes negative after the time interval Td. Then asstep 361 of FIG. 14B, steps 361a, 361c, 361f, .[.3621j.]..Iadd.361j.Iaddend., 361k, .[.361.]. .Iadd.361l .Iaddend.and 361o ofFIG. 14C are processed. At step 361o, the rear suspension characteristicis altered to the `SOFT` state and the flag FSF is reset. These are theprocess steps to actually alter the rear suspension characteristic adelay time Td after the judgment for performing that. Then a timer T3for returning the rear suspension characteristic is reset (361p),followed by steps 361q, 361r, 361s, 361t, 361u and 361v. Then theprocess steps being from B of FIG. 14A again.

Another case of the second embodiment is explained, the case beingreturning rear suspension characteristic by the first judgmentcondition, i.e. proceeding to step 361 of FIG. 14B with flags F1=0,FA=0, FH=0, FSP=0 and .[.FSf.]. .Iadd.FSF.Iaddend.=0. The process stepsproceed through 361a, 361b, 361e and 361h of FIG. 14D, and at step 361hthe delay time Td is put into the timer T6 and the flag FSP is set.

As described before, the process steps proceed through 361j, 361k, 361l,361q, 361r, 361s, 361u and 361v and then return to B of FIG. 14A. Inthis case, only the timer T6 becomes negative after a time interval Td,so the process steps proceed through 361a, 361b, 361e, 361j, 361k and361n, where the rear suspension characteristic is altered to the `SPORT`state and the flag FSP is reset. Then the process steps begin from B ofFIG. 14A again.

Another case of the second embodiment is explained, the case beingaltering by the second judgment condition, i.e. proceeding to step 361of FIG. 14B with flags F1=0, FA=1, FH=0, FSP=0 and FSF=0. The processsteps proceed through 361a, 361b, .[.36d.]. .Iadd.361d .Iaddend.and 361gof FIG. 14D, and at step 361g the delay time Td is put into the timer T7and the flag .[.FSH.]. .Iadd.FH .Iaddend.is set. As described before,the process steps proceed through 361j, 361k, .[.361h.]..Iadd.361l.Iaddend., 361q, 361s, 361t, 361u and .[.36v.]. .Iadd.361v.Iaddend.and then return to B of FIG. 14A.

In this case, only the timer T7 becomes negative after a timer intervalTd, so the process steps proceed through 361a, 361b, 361d, 361j, and361m, where the rear suspension characteristic is altered to the `HARD`state and the flag FH is reset. Then the process steps begin from B ofFIG. 14A again.

The case of returning the rear suspension characteristic by the secondjudgment condition, i,e, proceeding to step 361 of FIG. 14B with flagsF1=0, FA=0, FH=0, FSP=0 and FSF=0, is the same as the case of firstjudgment condition which is explained before.

Those process steps are so repeated. An example of control timingsperformed by the second embodiment is then explained with FIGS. 15 and16. Firstly, the case of altering and returning of rear suspensioncharacteristic by the first judgment condition is explained with FIGS.11A and 15. The front wheel W1R or W1L begins to move down into a smalldip O at a time point t1. At a time point t2, which is a time intervalts later than the time point t1, the ECU 300 judges that the largestfront vehicle height change h exceeds a corresponding reference valueh1. At a time point t23, which is a delay time Td after t2, the ECU 300drives the rear suspension alteration actuators 3d and 4d to alter therear suspension characteristic to a `SOFT` state. At a time point t5which is the time interval Ta after the time point t23 the rearsuspension characteristic has been altered to the `SOFT` state. The timepoint t5 coincides with the time point when the rear wheels W2R, W2Larrive at a small dip O. The driving signal from the ECU 300 is sent tothe actuators 3d and 4d until a time point t25.

At a time point t6, which is the delay time Tk for returning the rearsuspension characteristic after the time point t2 when the judgment ismade that the front wheel W1R or W1L moves down into the small dip O,the rear wheels W2R and W2L pass the small dip O and begin to move on aflat surface.

At a time point .[.T7.]. .Iadd.t7.Iaddend., which is a timer interval trlater than the time point t6, the ECU 300 judges that the largest frontvehicle height change hr is less than a corresponding reference valueh2. At a time point t28, which is a delay time Td after t7, the ECU 300drives the rear suspension alteration actuators 3d and 4d to alter therear suspension characteristic from the `SOFT` state to a `SPORT` state.The driving signal from the ECU 300 is sent to the actuators 3d and 4duntil a time point t30.

Another case of altering and returning of rear suspension characteristicjudgment condition is explained with FIG. 12A and FIG. 16. The frontwheel W1R or W1L begins to move down into a large dip P at a time pointt11. At a time point t12, which is a time interval T later than the time.[.pint.]. .Iadd.point .Iaddend.t11, the ECU 300 judges that the largestfront vehicle height change H exceeds a corresponding reference valueH1. At a time point t33, which is a delay time Td after t12, the ECU 300drives the rear suspension alteration actuators 3d and 4d to alter therear suspension characteristic to a `HARD` state. At a time point.[.T15.]. .Iadd.t15 .Iaddend.which is the time interval Ta after thetime point t33 the rear suspension characteristic has been altered tothe `HARD` state. The time point t15 coincides with the time point whenthe rear wheels W2R, W2L arrive at the large dip P. The driving signalfrom the ECU 300 is sent to the actuators 3d and 4d until a time pointt34.

At a time point t16, which is the delay time Tk for returning the rearsuspension characteristic after the time point t12 when the judgment ismade that the front wheel W1R or W1L moves down into the large dip P,the rear wheels W2R and W2L pass the large dip and begin to move on aflat surface.

At a time point t17, which is a time interval .[.tr.]. .Iadd.Tr.Iaddend.later that the time point t16, the ECU 300 judges that thelargest front vehicle height change Hr is less than a correspondingpreference value H2. At a time point t35, which is a delay time Td aftert17, the ECU 300 drives the rear suspension alteration actuators 3d and4d to alter the rear suspension characteristic from the `HARD` state tothe `SPORT` state or to the `SOFT` state. The driving signal from theECU 300 is sent to the actuators 3d and 4d until a time point t37.

The second embodiment of the present invention is so arranged asdescribed above that it has a following advantage besides that derivedfrom the first embodiment. The alteration of the rear suspension isrestricted only to necessary instances to maintian both thecontrollability and stability and the ride comfort as much as possibleby introducing the delay time for performing the rear suspensionalteration control after the front wheel passes a bump or a dip.

The third embodiment is hereinafter explained, an outline of whoseconstruction is illustrated in FIG. 17. A front vehicle height detectorM4 provided between a front wheel M2 and a body M3 of an automobiledetects the distance therebetween to generate and send a front vehiclesignal to a .[.hieght.]. .Iadd.height .Iaddend.data calculation meansM5. A plurality of height data are calculated in the height datacalculation means from the front vehicle height signal and sent to ajudgmant means M6, where each height data is compared with acorresponding reference value. When certain conditions are satisfied,the judgment means M6 generate a judgment result signal and send it to arear suspension characteristic alteration means M9 which drives rearsuspension between the rear wheels M8 and the body M3 to alter thecharacteristic according to the judgment result signal. While theconstruction described as far is the same as that of the first and thesecond embodiments, this third embodiment is provided with a vehiclespeed detection means M1 and a reference alteration means M7, whichalter the reference value of the judgment means according to the vehiclespeed. The construction or apparatus of the third embodiment is the sameas the first and the second embodiments. FIGS. 3, 4, 5, 6, and 8.

The process steps, which are performed by the ECU in this embodiment,are hereinafter described referring to flow charts shown in FIGS.18A-18F. The flow charts indicate the process steps performed by the ECUin response to the vehicle height sensor 1 of the digital type whichsends out a digital signal, as shown in FIG. 7.

The process steps are repeatedly performed in every predetermined timeinterval, such as 5 msec.

An outline of the process steps shown in the flow chart of FIG. 18A isdescribed as follows with step numbers in the parentheses:

Firstly initial setting is performed, i.e., all variables and all flagsare reset (410) except those storing the maximum and the minimum frontvehicle height, VHh and VHl. After waiting for a time interval Δt(420),a timer T1 is cleared (430). The timer T1 is counted up by anintermittent interrupt routine as shown in FIG. 18B, where other timersT2, T3, TC, TD, TE and TF are counted up.

A current front vehicle height VH(S)n is detected by the front vehicleheight sensors 1 and 2 (440) and a first preset time tR, a second presettime TR, a first maximum front vehicle height VHh, a first minimum frontvehicle height VHl, a second minimum front vehicle height VHL.Iadd.,.Iaddend.a second maximum front vehicle height VHH.Iadd., a.Iaddend.first tentative minimum front vehicle height VHh1, a firsttentative minimum front vehicle height VHl1, a second tentative minimumfront vehicle height VHL1 and a second tentative maximum front vehicleheight VHH1 are calculated (450). At step 450, the differences betweencorresponding maximum and minimum front vehicle heights are calculatedto make a first largest front vehicle height change h, a first tentativelargest front vehicle height change h1, a second largest front vehicleheight change H and a second tentative largest front vehicle heightchange H1. Then a front vehicle height change during a time interval twhich is shorter than a quarter of the cycle time of the front vehicleheight vibration is detected to get a speed of front vehicle heightchange (460). That is called a first detection process step. A seconddetection process step is to detect the largest front vehicle heightchange during a time interval T which is longer than a quarter of thecycle time of the front vehicle height vibration to get the amplitude(470). And lastly the damping force of shock absorbers 3a and 4a isaltered to a desired state according to the result of the first andsecond detection process steps (480).

Since the time intervals used in the first and the second detectionprocess steps are much longer than the cycle time needed to perform theroutine of steps 410-480 (i.e. 5 msec), two results of the first and thesecond detection process steps are not detected in every cycle of theroutine.

Details of steps 450-480 are hereinafter explained. After steps 410-440are performed as described before, the values TR, tR, VHh, VHl, h, VHh1,VHl1, h1, VHH, VHL, H, VHH1, VHL1 and H1 are calculated by the flowchart shown in FIG. 18C. The vehicle speed V is detected by the frontvehicle height sensor 250 (500) and the first maxinum front vehicleheight VHh for the first detection process steps is compared with thecurrent front vehicle height VH(S)n (502). If the current front vehicleheight VH(S)n is greater, the current value of the first maximum frontvehicle height VHh is replaced by the current front vehicle height(504), otherwise the first minimum front vehicle height VHl is comparedwith the current front vehicle height VH(S)n.

If VH(S)n<VHl, the value of VHl is replaced by the value of VH(S)n.Otherwise the process steps proceed to step 510. Seps 510-516 are theprocess steps for calculating the first tentative maximum front vehicleheight VHh1 and the first tentative minimum front vehicle height VHl1,which is similar to the prescribed steps 502-508. Also steps 518-524 arefor calculating the second maximum front vehicle height VHH and secondminimum front vehicle .[.vehicle.]. height VHL, steps 526-532 for thesecond tentative maximum front vehicle height VHH1 and the secondtentative minimum front vehicle height VHL1.

Lastly for the process steps of FIG. 18C, step 534 is performed. Herethe first largest front vehicle height change h is calculated as thedifference between the first maximum front vehicle height VHh and thefirst minimum front vehicle height VHl, a first tentative largest frontvehicle height change h1 as the difference between the first tentativemaximum front vehicle height VHh1 and the first tentative .[.manimum.]..Iadd.minimum .Iaddend.front vehicle height VHl1, a second largest frontvehicle height change H as the difference between the second maximumfront vehicle height VHH and the second minimum front vehicle height VHLand a second tentative largest front vehicle height change H1 as thedifference between the second tentative maximum front vehicle heightVHH1 and the second tentative minimum front vehicle height VHL1. Thefirst preset time tR and the second preset time TR are calculated fromthe vehicle speed V, the wheelbase A1 and compensatory terms A2 and A3as follows.

    tR=A1/V+A2

    TR=A1/V+A3

Here the compensatory terms A2 and A3 are determined from the responsetime of actuators 3d and 4d and front vehicle height sensors 1 and 2.

The first detection process steps are then explained with the flowchartof FIG. 18D. These process steps are for detecting a front vehicleheight change during a relatively small time interval t which isdetermined to be about a quarter of a cycle time of the front vehicleheight vibration in order to get a speed of front vehicle height change.

At step 500 it is judged which value a flag F1 is among `0`, `1`, `2`.The flag F1 represents the states of the damping force of the shockabsorbers 3a and 4a, `soft`, `sport` and `hard` respectively. Since atthe initial state the value is `0`, it is judged whether the timer T2has elapsed the time interval t (552). While T2<t this detection processsteps are repeated and no further action is made. When T2>=t isrealized, the timer T2 is cleared (554) and it is judged wheter thefirst largest front vehicle height change h is greater than acorresponding reference value f2(V) (556). If the result is NO, then itis judged whether h is greater than another corresponding referencevalue f1(V) (560). These reference values are illustrated in FIG. 19.The reference value f1(V) represents a boundary between the `soft` andthe `sport` states of the shock absorbers 3a and 4a and so determined toincrease as the decrease in the vehicle speed and to decrease as theincrease in the vehicle speed. Similarly f2(V) represents a boundarybetween the `sport` and the `hard` states of the shock absorbers and sodetermined to be higher than the f1(V) and increase according to thedecrease in the vehicle speed. Here the `soft` state of the shockabsorbers means that the damping force is weak to improve the ridecomfort by preventing the shock from the road surface vibrating thevehicle body. The `hard` state means that the damping force is strong toimprove the controllability and stability of the vehicle. The `sport`state is an intermediate state between the `soft` and the `hard` statessuited for a normal driving state.

In case h>=f2(V), the flag F1 is set to be `2` (558), and in casef2(V)>h>=f1(V), the flag F1 is set to be `1` (562). Then the timer TC iscleared, the values of VHh, VHl, VHh1 and VHl1 are replaced by the valueof the current front vehicle height VH(s) and h and h1 are cleared(566). Here the current cycle of the routine is finished.

Then the next routine begins from the judgment of the value of the flagF1 (550). If the flag F1 is `1` then it is judged whether the timer T2is greater than t (568). If T2<t, then it is judged whether the timer TCis greater than the first preset time tR (576). The first preset time tRis normally set to be larger than the time interval t. If it is judgedthat TC<tR here, the timer TD is cleared (578), the values of VHh1 andVHl1 are replaced by the current front vehicle height VH(S)n and h1 iscleared (580).

In the mean time when T2>=t (568), the timer T2 is cleared (570) and itis judged whether h>=f2(V) (572). If it is still f1(V)<=h<f2(V), thevalues of VHh and VHl are replaced by the current front vehicle heightVH(S)n and h is cleared (574). And if TC<tR yet, the steps 578 and 580are processed and the current routine is finished.

When it has become TC>=tR (576), it is then judged whether the timer TDis greater than the time interval t (582). If TD<t the current routineis finished but if TD>=t the timer TD is cleared (584) and it is judgedwhether h1<f1(V) (586). While h1<=f1(V), the routine is finished withthe process step of step 580. When it has become h1<f1(V), the flag F1is set to be `0` (588), the timer T2 is cleared, the values of VHh, VHl,VHh1 and VHl1 are replaced by the current front vehicle height VH(S)nand h and h1 are cleared (592).

That shows that when it has become f2(V)>h>=f1(V) with the state of theflag F1=0, it is set that F1=1 once, and after the time interval tR, ifh<f1(V), the flag F1 is again set to be `0`.

If it has become h>.[.f2(V).]. .Iadd.=f2(v) .Iaddend.within the timeinterval t (572), F1 is set to be `2` (594), the timer TC is cleared andthe step 592 is processed to finish the routine.

In the next routine, since F1=2, the timer TC is compared with the firstpreset time tR (598) and, until TC exceeds the first preset time tR, thetimer RD is cleared, the values of VHh1 and VHl1 are replaced by thecurrent front vehicle height VH(S)n and h1 is cleared (612). After thefirst present time tR, the .[.time.]. .Iadd.timer .Iaddend.TD and thetime interval t is compared (602), it is checked by every time intervalt in which domain h1 lies. When TD>=t (602) the timer TD is cleared(604) and the comparisons between h1 and f1(V) (606) and between h1 andf2(V) (610) are performed respectively.

If h1>=f2(V) (610), then the flag F1 is not changed. When h1 decreasesand it has become that f2(V)>h1>=f1(V) (610), the flag F1 is set to be`1`, the timers T2 and TC are cleared (614), the values of VHh, VHl,VHh1 and VHl1 are replaced by the current front vehicle height VH(S)nand h and h1 are cleared (616). When h1 is further decreased that it hasbecome h1<f1(V), the flag F1 is set to be `0` and the timer T2 iscleared (608).

The summary of the above process steps is as follows.

(1) When the speed of the front vehicle height change, which is thechange h (h1) in the front vehicle height during the time interval t,exceeds a reference value f1(V) which is determined according to thevehicle speed, the flag F1 is set to be `1` (562) and when it exceedsanother reference value f2(V), the flag F1 is set to be `2` (558) fromits original value of `0`. When h increases to become larger than f2(V)(572) after the flag F1 is set to be `1`, it is immediately set to be`2` (594).

(2) When h decreases to become less than f1(V) (586) after it is setF1=1, the first preset time tR is waited (576) and then it is set thatF1=0 (588).

(3) When h decreases to become less than f2(V) (610) after it is setF1=2, the first preset time tR is waited (598) and then it is set F1=1(614). When h further decreases to become less than f1(V) (606), thefirst preset time tR is waited (598) and then it is set F1=0 (608).

In the first detection process steps as described above, the alterationof the flag F1 which indicates the state of the shock absorber dampingforce is immediately done when it is altered to a higher value, while itis altered after the time interval tR when it is altered to a lowervalue. This is so arranged because the operations for alteration of thedamping force should be done immediately to adequately cope with thebump or dip of the road surface, while the returning operations areneeded a definite time later regarding the lag time due to thewheelbase.

The first tentative largest front vehicle height change h1 is calculatedfrom VHh1 and VHl1 besides h because it is needed to store the frontvehicle height changes separately for in case of the process steps forreturning to F1=0 (576-592) and for in case of the process steps forgoing to F1=2 (568-572, .[.584.]. .Iadd.594.Iaddend., 596) when it isjudged that F1=1 at step 550, since there is a time difference of thefirst preset time tR in the beginning of the front vehicle heightdetection.

The second detection process steps is hereinafter explained with FIG.18E. In these process steps, F1 corresponds to F2, T2 to T3, t to T, tRto TR, TC to TE, TD to TF, f1(V) to F1(V), f2(V) to F2(V), VHh to VHH,VHl to VHL, VHh1 to VHH1, VHl1 to VHL1, h to H and h1 to H1 respectivelyof the variables described above. And the steps also correspond to thoseof FIG. 18D when the last two digits of the step numbers coincide witheach other. The summary of the second detection process steps is asfollows.

(1) When the amplitude of the front vehicle height vibration which isthe change H (H1) in the front vehicle height during the time intervalT, exceeds a reference value F1(V) which is determined according to thevehicle speed V, the flag F2 is set to be `1` (662) and when it exceedsanother reference value F2(V), the flag F2 is set to be `2` (658) fromits original value of `0`. When H increases to become larger than F2(V)(672) after the flag F2 is set to be `1`, it is immediately set to be`2` (694).

(2) When H decreases to become less than F1(V) (686) after it is setF2=1, the second preset time TR is waited (676) and then it is set F2=0(688).

(3) When H decreases to become less than F2(V) (710) after it is setF2=2, the second preset time TR is waited (698) and then it is set F2=1(714). When H further decreases to become less than F1(V) (706), thesecond preset time TR is waited (698) and then it is set F2=0 (708).

In the second detection process steps as described above, the alterationof the flag F2 which indicates the state of the shock absorber dampingforce is immediately done when it is altered to a higher value, while itis altered after the time interval TR when it is altered to a lowervalue, just as same as the case of the first detection process steps. Inthis second detection process steps, the time interval T is longer thanthe time interval t and is between a quarter and a full cycle time ofthe front vehicle height vibration. This process steps are so arrangedto detect the amplitude of the front vehicle height vibration. Therelationships between F1(V), F2(V) and the vehicle speed V .[.is.]..Iadd.are .Iaddend.shown in FIG. 20. The second preset time TR may bethe same as the first preset time tR, or it may be either longer orshorter, depending on the occasion.

The damping force alteration process steps as the last process steps areexplained with FIG. 18F. The flag F2 is judged (750) at first and if thevalue is `0` then the flag F1 is judged (752). If the value is `0`, itis judged whether the current state of the shock absorbers 3a and 4a isthe `soft` state (754). If the result is NO, the actuators 3d and 4d aredriven to make the damping force of the shock absorbers weak. Otherwisethe process steps are finished.

If the flag F1 is `1` at step 752, it is judged whether the state of therear shock absorbers 3a and 4a is the `sport` state (760). If the resultis NO, the actuators are driven to make the damping force of the shockabsorbers 3a and 4a normal. Otherwise the process steps are finished.

If the flag F1 is `2` at step 752, it is judged whether the state of therear shock absorbers 3a and 4a is the `hard` state (764). If the resultis NO, the actuators are driven to make the damping force of the shockabsorbers 3a and 4a strong. Otherwise the process steps are finished.

If the flag F2 is `1` at step 750, it is judged whether the flag F1 is`2` (758). If the result is NO, the shock absorbers are made to be inthe `sport` state or, if it is already in the `sport` state, kept to bein the `sport` state (762). Otherwise, if the flag F1 is `2`, they aremade to be in the `hard` state or, if the state is already `hard`, arekept to be in the `hard` state (766).

The damping force of the rear shock absorbers 3a and 4a are thuscontrolled according to the values of flag F1 by the first detectionprocess steps or of the flag F2 by the second detection process steps.

The process steps are then explained with the aid of the time charts ofFIGS. 21A-21C, which show the timings of (a) the current front vehicleheight VH(S)n, (b) the actuator drive signal, (c) the state of the rearshock absorbers and (d) the rear vehicle height.

In the case of FIG. 21A, front wheels of a vehicle begin to move down ina dip of a road surfece at a time point t1. Since then the current frontvehicle height VH(S)n increases sharply and if the first largest frontvehicle height change h during the time interval t which is between timepoints t2 and t3, exceeds f1(V), it is set that F1=1 by the firstdetection process steps (562). Since the flag F2 is `0` by the initialsetting, the rear shock absorbers are altered to the `sport` state(762). From the time point t3 the drive signal is sent to the actuators3d and 4d and is terminated at a time point t5, the alteration operationof the actuators are finished at the time point t4 which is between thetime points t3 and t5. After that, at a time point of t6 which is a timeinterval tc later than the time point t1, the rear wheels begin to movedown into the dip, where tc is determined as A1/V, A1 being thewheelbase and V being the vehicle speed.

If the first largest front vehicle height change h does not exceed f2(V)from the time point t3 until a time point t7, the interval being tR, thefirst tentative largest front vehicle height change h1 during the timeinterval t is detected from the time point t7. If h1 is less than f1(V)(586), it is set that F1=0 (588), the actuator drive signal is sent at atime point t8 which is the time interval t later than the time point t7to the actuators and the damping force of the rear shock absorbers 3aand 4a is altered at a time point t9 from the `sport` state to the`soft` state. At a time point t10 the actuator drive signal isterminated. In summary, the damping force of the rear shock absorbersare altered according to the first vehicle height data, i.e. the firstlargest front vehicle height change h during the time interval t, andthen after the time interval tR, when the rear wheels have alreadypassed the bump or dip, the damping force is corrected according to thesecond vehicle height data, i.e. the first tentative largest frontvehicle height change h1 during the time interval t.

In the case of FIG. 21B, front wheels of a vehicle begin to move down ina dip of a road surface at a time point t11. Since then the currentfront vehicle height VH(S)n increases sharply and if the second largestfront vehicle height change H during the time interval T, which isbetween time points t12 and t13, exceeds F2(V), it is set that F2=2 bythe second detection process steps (658). If the flag F1 is `0` by thefirst detection process steps, the rear shock absorbers are altered tothe `hard` state (766). From the time point t13 the drive signal is sentto the actuators 3d and 4d and is terminated at a time point t15, thealteration operation of the actuators are finished at the time point t14which is between the time points t13 and t15. After that, at a timepoint of t16 which is a time interval tc later than the time point t11the rear wheels being to move down into the dip.

If the second largest front vehicle height change H during the timeineterval T does not exceed F2(V) from the time point t13 to a timepoint t17, the interval being TR, the second tentative largest frontvehicle height change H1 during the time interval T is detected from thetime point t17. If H1 is less than F1(V) (706), it is set that F2=0(708), the actuator drive signal is sent at a time point t18 which isthe time interval T later than the time point t17 to the actuators andthe damping force of the rear shock absorbers 3a and 4a is altered at atime point t19 from the `hard` state to the `soft` state. At a timepoint t20 the actuator drive signal is terminated. In summary, thedamping force of the rear shock absorbers is altered according to thefirst vehicle height data, i.e. the second largest front vehicle heightchange H during the time interval T, and then after the time intervalTR, when the rear wheels have already passed the bump or dip, thedamping force is corrected according to the second vehicle height data,i.e. the second tentative largest front vehicle height change H1 duringthe time interval T.

In the case of FIG. 21C, which explains the case that the two dampingforce alteration operations by the first and the second detectionprocess steps are performed in combination, front wheels of a vehiclebegin to move down in a dip of a road surface at a time point t21. Sincethen the current front vehicle height VH(S)n increases sharply and ifthe first largest front vehicle height change h during the time intervalt, which is between time points t22 and t23, exceeds f1(V), it hasbecome F1=1 by the first detection process steps (562). Since the flagF2 is `0` by the initial setting, the rear shock absorbers are alteredto the `sport` state (762). From the time point t23 the drive signal issent to the actuators 3d and 4d.

If the second largest front vehicle height change H during the timeinterval T exceeds F2(V) from the time point t22 to a time point t23, itis set that F2=2 by the second detection process steps (658). So, thoughthe flag F1 is `1`, the rear shock absorber is altered to be the `hard`state (766). From the time point t26 the actuator drive signal is sentand the hardening operation is finished at a time point t28. Theactuator drive signal is terminated at a time point t29. During that, ata time point t27 which is a time interval tc later than the time pointt21 the rear wheels begin to move down in the dip.

After that, at a time point t30 which is a time interval tR later thanthe time point t23, the value of h1 is checked by every time interval tby the first detection process steps (584). As h1 is already less thanf1(V), it is set that F1=0 (588). Since, however, this time point isstill within the time interval of TR+T from the time point t26, it ismaintained that F2=2 until a time point t32 (698). So at the dampingforce alteration judgement (750), the `hard` state is maintained and thevehicle body vibration is detered to keep the controllability andstability good.

After that, from a time point t31, the value of H1 is checked by everytime interval T by the second detection process steps (706). As H1<F1(V)at first of the process steps, it is set that F2=0 (708). So, since F1=0already, the shock absorbers are altered to be in the `soft` state bythe damping force alteration process step (756). In this combinedprocess steps, firstly the rear shock absorber damping force is alteredaccording to the first largest front vehicle height change h during thetime interval t by the first detection process steps and then it iscorrected according to the second largest front vehicle height change Hduring the time interval T by the second detection process steps. Andfurther correction of the damping force is made after the time intervalTR.

As described above, the third embodiment of the present inventiondetects the speeds of the front vehicle height change h and h1 and therear suspension characteristic is controlled by judging h1 with thereference values, f1(V) and f2(V), and H1 with F1(V) and F2(V). Theembodiment is so arranged that the controllability and stability of thevehicle can be maintained and the rear portion of the vehicle isprotected from being shocked. With the use of the speed of the frontvehicle height change h and h1 a quick response or alteration of therear suspension characteristic against sporadic bumps or dips of theroad surface is made, and with the use of the amplitude of the frontvehicle height change H and H1 the alteration is corrected to keep thecontrol more precise and adequate to the disturbance. Besides that, asthe reference values are determined according to the vehicle speed, thecontrol is maintained at further wide situations. Since the referencevalues, f1(V) and f2(V) corresponding to h and h1 and F1(V) and F2(V)corresponding to H and H1, are made to be two separate values, thecontrol can well cope with the size of the bump or dip.

While in the third embodiment, the suspension characteristic is alteredby altering the damping force of the rear shock absorbers, it is alsorealized by the alteration of the spring contact of rear air suspensionsinto three different states, also `soft`, `sport` and `hard`. That isdone actually by changing the cmmunication passage between the main airchambers 3b and 4b and the auxiliary air chambers 3c and 4c with the useof the large diameter air passages 70 and the small diameter air passage74 of the valve unit 44 (FIG. 5). The two means, the shock absorbers andthe air suspensions, can be used simultaneously to alter the rearsuspension characteristic.

Instead of the speed of front vehicle change used in the embodiment, anacceleration of that may be used to judge the bump or dip, which has amerit of detecting them at the earliest stage of the moving up or downof the front wheels.

The fourth and the fifth embodiments of the present invention arehereinafter described.

FIG. 22 shows an outline of the embodiments. These embodiments include areference alteration means i which alters the reference value used in ajudgment means g.

A front vehicle height detector e is provided between the body and thefront wheels d of an automobile to detect the distance therebetween andgenerate and send vehicle height data to the judgment means g. Thejudgment means g compares the vehicle height data with correspondingreference values, which can be altered by the alteration means idepending on the vehicle speed detected by a speed sensor f.

A judgment result signal is generated according to the comparison by thejudgment means g and is sent to a rear suspension characteristicalteration means, which alters rear suspensions c provided between thebody and rear wheels b.

FIG. 23A shows a schematic figure of an automobile passing a bump 1,FIG. 23B shows a relationship of a piston speed of a shock absorber anda vehicle speed V and FIG. 23C shows time charts corresponding to thecase of FIG. 23A. The figures are for explaining an abstract of theprocess steps performed by the fourth and the fifth embodiments.

The moving speed of a piston of a shock absorber generally increasesaccording to an increase in the running speed of an automobile as FIG.23B. A change in the front vehicle height during a definite timeinterval ts increases as the automobile speed increases, as shown inFIG. 23C, whose upper part shows a time chart of the change of the frontvehicle height when the automobile is running with relatively low speedand the lower chart shows that when it is running with relatively highspeed.

The front vehicle height change of lower automobile speed .[.H1.]..Iadd.Hl .Iaddend.is less than that of higher speed Hh. This indicatesthat the conditions of the automobile is different when it runs with ahigher speed and when with a lower speed. So the speed sensor f isprovided to alter the judging condition of the judgment means gaccording to the speed of an automobile j to detect, for example, a bump1 of a road surface k.

The construction of the apparatus of these embodiments is the same asthat of the first embodiment as shown in FIGS. 3-8. But the processsteps performed by the ECU 300 is different and are shown by theflowcharts of FIGS. 24A-24D for the fourth embodiment and of FIGS.28A-28D for the fifth embodiment.

An outline of the process steps of the fourth embodiment is describedreferring to FIG. 24A as follows.

(1) Current front vehicle height VH(S)n is detected (808).

(2) a reference value h1 is calculated using the current vehicle speed V(810).

(3) It is judged whether a front vehicle height change during a definitetime interval exceeds the reference value h1 (822).

(4) If the front vehicle height change exceeds the reference value h1,the rear suspension characteristic is altered (834).

The alteration of rear suspension characteristic means, if the drivingcondition is that requires especially preventing shocks at the rearpassenger seat, alteration to a `SOFT` state. In definite, the actuators3d and 4d are driven to connect the main air chambers 3b and 4b and theauxiliary air chambers 3c and 4c, respectively, or the damping forces ofthe shock absorbers 3a and 4a are decreased. If, on the other hand, thedriving condition is that the controllability and stability are to berequired against large vibrations due to the road surfaceirregularities, the alteration of the rear suspension characteristicmeans the alteration to a `HARD` state. In definite, the main airchambers 3b and 4b and the auxiliary air chambers 3c and 4c aredisconnected to make the spring constant of the rear air suspensionshigh or the damping forces of the shock absorbers 3a and 4a areincreased.

The above-mentioned items (1)-(4) are the main process steps forproducing the effect of the present invention through the fourthembodiment. In addition, other process steps are performed in thisembodiment as follows:

(5) Subsequently to the item (4), the characteristic of the rear wheelsuspensions is returned to the original state if the front vehicleheight is within a predetermined range after a predetermined timeinterval (826-834).

The process steps in the fourth embodiment are hereinafter described indetail. It is judged firstly whether or not the process steps are beingperformed for the first time since the activation of the ECU 300 (800).If the process steps are judged to be being performed for the first timesince the activation of the ECU 300, initial setting is performed (802),all variables are cleared and all flags are reset. After the initialsetting is performed .[.(800).]. (.Iadd.802) .Iaddend.or if the processsteps in the routine are judged to be performed for the second time orlater since the activation of the ECU 300, it is judged whether asampling time interval t has elapsed (804). The time interval t is apreset smallest time interval for sampling vehicle height data, as shownin FIG. 25. A timer T1 is counted at step 840 in the intermittentinterrupt routine process steps of FIG. 24B. When the timer T1 elapsesthe time interval t, the timer T1 is reset (806) and a current frontvehicle height VH(S)n is input from the front vehicle height sensors 1and 2 (808).

Then a delay time Tr for returning the rear suspension characteristic isdetermined and the maximum front vehicle height VHh and the minimumfront vehicle height .[.VH1.]. .Iadd.VHl .Iaddend.during the timeinterval t are determined (810). Also a reference value h1 for beginningthe control and another reference value h2 for terminating the controlare calculated (810).

Details of this step 810 are explained with FIG. 24C as follows. Firstlyit is judged whether the current front vehicle height VH(S)n exceeds thepast maximum front vehicle height VHh (810a).

If the result is YES, a new maximum front vehicle height VHh isdetermined to be the current front vehicle height VH(S)n (810b).Otherwise it is judged whether the current front vehicle height VH(S)nis less than the past minimum front vehicle height .[.VH1.]..Iadd.VHl.Iaddend.(810c). If the result is YES, a new minimum frontvehicle height .[.VH1.]. .Iadd.VHl .Iaddend.is determined to be thecurrent front vehicle height VH(S)n (810d). Otherwise and after step810b or 810d is performed, the vehicle speed V is detected by thevehicle speed sensor 250(810e) and the delay time Tr is calculated(810f) as

    Tr=WB/V+A2,

where WB is wheelbase of the vehicle, V is the vehicle speed and A2 is acompensatory term regarding to a detection lag and passing time. Thereference values h1 and h2 are determined, by the use of presetrelationships as shown by FIG. 26, according to the vehicle speed V(810g). They are so determined to increase as the vehicle speed Vincreases and it is always set that h1>h2. The relationship between h1and V is represented by a function f1 and that between h2 and V isrepresented by a function f2, as in FIG. 26.

Returning to FIG. 24A, it is judged whether the vehicle is running bycomparing the current vehicle speed V and a reference preset value VO(812) and only when the vehicle is running, further process steps areperformed. Then it is judged whether `AUTO` mode is selected by thedriver (814). If the `AUTO` mode is selected, then it is judged whethera flag F1 is set (816), which indicates that the rear suspensioncharacteristic is in the altered state. This time, as F1=0, step 818 isselected and it is judged whether a timer T2 exceeds a time interval tsfor judging the front vehicle height. The time interval ts is determinedas a product of the sampling time interval t and an integer as shown inFIG. 25. The timer T2 is counted at step 840 in the intermittentinterrupt routine process steps of FIG. 24B. When the timer T2 elapsesthe time interval ts, the timer T2 is reset (820). Then it is judgedwhether the largest front vehicle height change VHh-VHl during the timeinterval ts exceeds the corresponding reference value h1 for beginningthe alteration control (822). If the result is YES, the flag F1 is set(824) and the maximum front vehicle height VHh and the maximum frontvehicle height VHl are replaced by the current front vehicle heightVH(S)n (832). Then at step 834 the rear suspension characteristicalteration actuators are driven. Details of the step 834 are explainedwith FIG. 24D as follows.

It is judged whether the flag F1 is set (834a) and, since this timeF1=1, it is judged whether a flag FSF is set (834d). The flag FSFindicates that the rear suspension characteristic is in the `SOFT`state. Since this time FSF=0, the rear suspension characteristic isaltered to the `SOFT` state, the flag FSF is set and a flag FSPrepresenting the `SPORT` state is reset (.Iadd.834e), and a timer T3 isreset .Iaddend.(834f). Those are details of step 834 and the processstep returns to step 800 in FIG. 24A.

After executing steps 800-814, step 826 is selected at step 816, sinceF1=1 this time. It is judged whether a timer T3 exceeds a delay time Trfor returning the rear suspension characteristic (826). The timer T3 iscounted at step 840 in the intermittent interrupt routine process stepsof FIG. 24B. When the timer T3 exceeds Tr (826), it is judged whetherthe timer T2 exceeds a time interval ts. The timer T2 is counted at step840 in the intermittent interrupt routine process steps of FIG. 24B.When the timer T2 elapses the time interval ts, the timer T2 is reset(828). Then it is judged whether the largest front vehicle height changeVHh-VHl during the time interval ts is less than a correspondingreference value h2 for returning control (829). If the result is YES,the flag F1 is reset (830) and the maximum front vehicle height VHh andthe minimum front vehicle height VHl are replaced by the current frontvehicle height VH(S)n (832). And at step 834, the rear suspensioncharacteristic alteration actuators are driven, whose details areexplained with FIG. 24D as follows.

It is judged whether the flag F1 is set (834a) and, since this timeF1=0, then it is judged whether a flag FSP is set (834b). Since thistime FSP=0, the rear suspension characteristic is altered to the `SPORT`state, the flag FSP is set and the flag FSF is reset (834c). Then atimer T3 for counting a delay time until returning the rear suspensioncharacteristic is reset .[.(8345).]. (.Iadd.834f).Iaddend.. Those aredetails of step 834 and the process steps returns to step 800 of FIG.24A.

The routines as described above are processed repeatedly.

An example of control timings performed by the fourth embodiment is thenexplained with FIGS. 27A and 27B. FIG. 27A shows an automobile j whosefront wheel W1R or W1L is passing a dip m of a road surface k with aspeed V. FIG. 27B shows time charts of the output of the front vehicleheight sensor 1 or 2, the drive signal for the rear suspensioncharacteristic alteration actuators 3d and 4d, the rear suspensioncharacteristic and the rear vehicle height.

The front wheel W1R or W1L begins to move down into the dip m at a timepoint t1, Since .Iadd.then, .Iaddend.the output VH(S)n of the frontvehicle height sensor 1 or 2 becomes large. From the time point t1, thefront vehicle height is sampled every time interval t as shown in FIG.25, and the maximum front vehicle height VHh and the minimum frontvehicle height VHl during the time points t2 and t3. The differenceVHh-VHl is the largest front vehicle height change during the timeinterval ts. The reference values h1 and h2 are determined as in FIG. 26according to the vehicle speed.

At the time point t3, the ECU 300 judges that the largest front vehicleheight change h exceeds a corresponding reference value h1. At this timepoint, the ECU 300 drives the rear suspension alteration actuators 3dand 4d to alter the rear suspension characteristic to a `SOFT` state,i.e. the main air chambers 3b and 4b are connected with the auxiliaryair chambers 3c and 4c, respectively.

The alteration operation is finished at a time point t4, a time intervalTa later than t3. The driving signal from the ECU 300 is sent to theactuators 3d and 4d until a time point t5, through the alterationoperation per se is finished before at the time point t4. Between thetime point t1 and a time point t6, which is a time interval Tc laterthan the time point t1, the rear wheels W2R, W2L begin to move down intothe dip m. Here the time interval Tc is that for the front and rearwheels to pass the dip.

So the time point t4 should be before the time point t6.

At a time point t7, which is a time interval Tr after the time point t3,the rear wheels W2R, W2L have passed the dip m.

At a time point t8, which is a time interval ts later than the timepoint t7, the ECU 300 judges that the largest front vehicle heightchange VHh-VHl is less than a corresponding reference value h2. At thistime point, the ECU 300 drives the rear suspension alteration actuators3d and 4d to alter the rear suspension characteristic from the `SOFT`state to the `SPORT` state, i.e. the main air chambers 3b and 4b aredisconnected with the auxiliary air chambers 3c and 4c, respectively.

The alteration operation is finished at a time point t9, a time intervalTa later than t8. The driving signal from the ECU 300 is sent to theactuators 3d and 4d until a time point t10, through the alterationoperation per se is finished before at the time point t9.

As described above, the fourth embodiment is so arranged that shocks areprevented at the rear part of the automobile and ride comfort thereof iskept good in passing sporadic bumps or dips. And after passing them, thesuspension characteristic is returned to fit to a normal road surface tomaintain the controllability and stability. In the above embodiment, therear suspension characteristic is altered to `SOFT` and `SPORT` statesaccording to the judgment results, the alteration steps may be more byso arranging the air suspensions or shock absorbers or combining thevarious characteristics of every component.

As the reference values for comparing the largest front vehicle heightchanges is altered depending on the vehicle speed in the fourthembodiment, the rear suspension characteristic is altered adequately atany driving speed. And because the reference values are increasedaccording to the vehicle speed, the number of occurences of the rearsuspension characteristic alteration decreases as the vehicle speedincreases, which leads to a merit of prolonged duration of theactuators. The two reference values are set to be different forpreventing the hunting of the rear suspension alteration control.

The fifth embodiment of the present invention is then explained withflow charts of FIGS. 28A, 28B, 28C, 28D and 28E, schematic illustrationof FIG. 29A and timing charts of FIG. 29B. The construction of theapparatus of this embodiment is the same as that of the firstembodiment, as FIGS. 3-8. The flow charts of this embodiment is so madeto correspond to that of fourth embodiments, as FIGS. 24A-24D, with thestep member 50 larger than the corresponding counter part, and thedenotation of the time points by this embodiment are made to be the sameas those of the fourth embodiment when those denote similar time points.

The main difference between the fourth and the fifth embodiments lies inthe timing to alter the rear suspension characteristic. While in thefourth embodiment the alteration control is performed as soon as thefront vehicle height change exceeds the corresponding reference value,it is performed just before the rear wheels pass the bump or dip in thisembodiment. For that purpose, a delay time Td, which is a time intervalbetween the detection of the bump or dip by the front vehicle heightsensors and the beginning of the rear suspension characteristicalteration control, is introduced in the fifth embodiment.

The steps 850-858 in the flow chart of FIG. 28A are the same as thecounterparts steps 800-808 in FIG. 24A of the fourth embodiment. At step861, a delay time Tr, the maximum front vehicle height VHh and theminimum front vehicle height VHl during the time interval ts, thereference value h1 for beginning the control and the other referencevalue h2 for terminating the control are calculated as the fourthembodiment. Besides those, the delay time Td is calculated in this step..[.For that purpose, a delay time Td, which is a time interval betweenthe detection of the bump or dip by the front vehicle height sensors andthe beginning of the rear suspension characteristic alteration control,is introduced in the second embodiment.

The steps 300-308 in the flow chart of FIG. 14A is the same as thecounterparts in FIG. 10A of the first embodiment. At step 311, a delaytime Tk, the maximum front vehicle height VHh of the first judgmentcondition, the minimum front vehicle height VHl of the first judgmentcondition, the maximum front vehicle height of the second judgmentcondition VHH and the minimum front vehicle height of the secondjudgment condition VHL are calculated as the first embodiment as well asthe delay time Td..]. Details of the step 861 are shown in FIG. 28C,where steps 861a-861g, are the same as steps 810a-810g of FIG. 24C. Atstep 861h, the delay time Td is calculated as

    Td=WB/V-A1-Ta,

where WB is a wheelbase, V is a vehicle speed, A1 is a compensatory termand Ta is a duration time of driving signal to the actuators to alterthe rear suspension characteristic.

Steps 862-882 of FIG. 28A are the same as steps 812-832 of FIG. 24A.Details of step 885, where the rear suspension characteristic is alteredafter a delay time Td, are hereinafter described with FIG. 28D.

It is judged whether the flag F1 is set (885a) and, since this timeF1=1, it is judged whether a flag FSF is set (885d). The flag FSFindicates that the rear suspension characteristic is in the `SOFT`state.

Since this time FSF=0, then at step 885e the delay time Td is put into atimer T5 and the flag FSF is set, where T5 is a timer which is counteddown by an intermittent interrupt routine step 890 of FIG. 28B. Since T5is non-negative and T4 is also non-negative, the process steps proceedthrough 885f, 885h and 885k, since FSP=0 at step 885k, 2×Td is put intothe timer T4. then since FSF=1 (885m), the process steps of step 885 arefinished and process steps being from 850 of FIG. 28A again. Though inthese process steps the timers t4 and T5 are counted down (890), thetimer t4 is renewed by a value 2×Td every time, preventing it from beingnegative. The timer T5, on the other hand, is not renewed by theseroutines, so it becomes negative after the time interval Td. Then asstep 885 of FIG. 28A, steps 885a, 885d and 885f of FIG. .[.28d.]..Iadd.28D .Iaddend.are processed. Since the timer T5 is negative, step885g is processed. The rear suspension characteristic is altered to the`SOFT` state and the flag FSF is reset. Those are the process steps toactually alter the rear suspension characteristic a delay time Td afterthe judgment for performing that. Then a timer T3 for returning the rearsuspension characteristic is reset (885j), the process steps begin from850 of FIG. 28A again. The following process steps which go throughsteps 854, 566, 880, 882 and 885 are the same as the case of the fourthembodiment.

When the process steps come to step 885 with F1=0, the process stepsproceed through 885a, 885b and 885c, of FIG. 28D, and at step 885c thedelay time Td is put into the timer T4 and the flag FSP is set.

As described before, the process steps proceed through 885f, 885h, 885k,885m and 885n. At step 885n, the value 2×Td is put into the timer T5 andthe process steps return to 850 of FIG. 28A. The timers T4 and T5 arecounted down at step 890 of FIG. 28B by every cycle of routine. Thistime T5 is renewed but T4 decreases every time and become negative afterthe time interval Td. The process steps at step 885 this time is asfollows. The process steps proceed through 885a, 885b, 885f and 885h ofFIG. 28D, and at step .[.885h.]. .Iadd.885i .Iaddend.the rear suspensioncharacteristic is altered to the `SPORT` state and the flag FSP isreset. As described before, the process steps proceed through 885j,885k, 885l, 885m and 885n and then return to step 850 of FIG. 28A.

An example of control timings performed by the fifth embodiment is thenexplained with FIGS. 29A and 29B. FIG. 29A shows an automobile j whosefront wheel W1R or W1L is passing a dip m of a road surface k with aspeed V, just as FIG. 27A. FIG. 29B shows similar time charts as thoseof FIG. 27B.

The front wheel W1R or W1L begins to move down into the dip m at a timepoint t1. Since then the output VH(S)n of the front vehicle heightsensor 1 or 2 becomes large. At a time point t3, which is a timeinterval ts later than the time point t2, the ECU 300 judges that thelargest front vehicle height change exceeds a corresponding referencevalue h1. Then at a time point t11, which is the time interval Td laterthan the time point t3, the ECU 300 drives the rear suspensionalteration actuators 3d and 4d to alter the rear suspensioncharacteristic to a `SOFT` state. The alteration operation is finishedat a time point t6, a time interval Ta later than t11. The time point T6coincides with the time point at which the rear wheels of the vehiclecome to the dip m.

The driving signal from the ECU 300 is sent to the actuators 3d and 4duntil a time point t12. At at time point t8 which is a time interval tsafter a time point t7 the ECU 300 judges that the largest front vehicleheight change is less than a corresponding reference value h2. The timepoint t7 is determined to be a time interval Tr later than the timepoint t3, as in the fourth embodiment. At a time point t13 which is thetime interval Td later than the time point t8, the ECU 300 drives therear suspension alteration actuators 3d and 4d to alter the rearsuspension characteristic from the `SOFT` state to the `SPORT` state.The alteration operation is finished at a time point t14 which is thetime interval Ta later than the time point t13. The driving signal fromthe ECU 300 is sent to the actuators 3d and 4d until a time point t15.

The fifth embodiment of the present invention is so arranged asdescribed above that is has a following advantage besides that derivedfrom the fourth embodiment. The alteration of the rear suspensioncharacteristic is restricted only to necessary instances to keep boththe controllability and stability and ride comfort good as much aspossible by introducing the delay time for performing the rearsuspension characteristic alteration control after the front wheelpasses a bump or a dip.

In the fourth and the fifth embodiments, the time interval for samplingvehicle data, i.e. the largest front vehicle height change, is fixed butthe reference values are increased according to the increase in thevehicle speed. The same effect is derived from by shortening thesampling time interval, while the reference values are fixed.

Examples of other rear suspension characteristic alteration means notfor any air suspension or shock absorber are described below. The firstexample is a bush for a joint of a suspension bar such as the upper andlower control arms of a suspension, as shown in FIGS. 31A and 31B. Thebush is provided with a mechanism for changing the stiffness of the bushto alter the characteristic of a suspension. The changing of thestiffness means that of the spring constant or damping force of thebush.

FIG. 31A shows a longitudinal sectional view of the joint of thesuspension bar. FIG. 31B shows a sectional view along a lineXXXIB--XXXIB shown in FIG. 31A. A control arm 901 extends along an axis904 perpendicular to the axis 902 is welded around the hole 905 at oneend of the control arm 901. An outer cylinder 908 having a hole 907 ispress-fitted in the sleeve 906. An inner cylinder 909 is provided in theouter cylinder 908 concentrically thereto. The bush 910 made ofvibrationproof rubber is interposed between the outer cylinder 908 andthe inner cylinder 909. The bush 910 and the outer cylinder 908 defineopenings 911 and 912 which are located in the face of each other alongthe axis 902 and extend as arcs around the axis 904, so that thestiffness in the direction of the axis 902 is set at a relatively lowvalue.

The hole 903 of the control arm 901 constitutes a cylinder whichsupports piston 913 movably back and forth along the axis 902. A sealingmember 914 is tightly packed in between the piston 913 and the insidesurface of the hole 903. A contact plate 916 is secured at one end ofthe piston 913. The contact plate .[.1916.]. .Iadd.916 .Iaddend.curvesabout the axis 904 and extends along the axis so that the plate isbrought into contact with the inside surface 915 of the opening 911.

The same construction as shown in FIGS. 31A and 31B is provided at theother end of the control arm 901. A cylinder chamber 917 is definedbetween the piston 913 and another piston not shown in the drawings andfitted with the other end of the control arm 901. The cylinder chamber917 connects with the exterior through a tapped hole 918 provided in thecontrol arm 901. A nipple 923 secured on one end 922 of a conduitconnected to an oil pressure source not shown in the drawings is securedin the tapped hole 918 to apply oil pressure to the cylinder chamber917. When the oil pressure in the cylinder chamber 917 is relativelylow, the force pushing the piston 913 leftward as to the drawings is soweak that the piston is held in such a position shown in the drawingsthat the contact plate 916 is brought into light contact with the innersurface 915 of the bush 910. As a result, the stiffness of the bush 910in the direction of the axis .[.903.]. .Iadd.902 .Iaddend.is relativelylow.

When the oil pressure in the cylinder chamber 917 is relatively high,the piston 913 is driven leftward as to the drawings and the contactplate 916 pushes the inner surface 915 of the bush 910 so that theportion of the bush between the contact plate and the inner cylinder 909is compressed. As a result, the stiffness of the bush 910 in thedirection of the axis 902 is heightened.

If the suspension bar is provided between the body and rear wheel of avehicle, the characteristic of the suspension for the rear wheel can bealtered by regulating the oil pressure in the cylinder chamber 917through the action of an actuator such as a pressure control valve. Whenthe oil pressure is heightened by an instruction from an ECU 300, thestiffness of the bush 910 is enhanced to increase the damping force andspring constant of the suspension to improve the controllability and thestability of the vehicle. When the oil pressure is lowered, the shock atthe rear portion of the vehicle is reduced.

The second example is another bush shown in FIGS. 32A and 32B and havingthe same function as the former. FIG. 32A shows a longitudinal sectionalview of the bush constructed together with an inner and an outercylinders as a bush assembly. FIG. 32B shows a sectional view along aline .[.XXXII.]. .Iadd.XXXIIB.Iaddend.--XXXIIB shown in FIG. 32A. Fourexpansible and compressible hollow bags 1010, which extend along an axis1003 and are separately located in equiangular positions around theaxis, are embedded in the bush 1005, and define four chambers 1011extending along the axis 1003 and separately located in equiangularpositions around the axis. Each hollow bag 1010 is secured at one end onone end of a coupler 1012 embedded in the bush 1005, by a clamp 1013, sothat the chamber 1011 connects with the exterior of the bush through thecoupler 1012. One end of a hose 1015 is fixedly connected to the otherend of the coupler 1012 by clamp 1014, and the other end of the hose1015 is connected to a compressed air source through an actuator such asa pressure control valve not shown in the drawings, so that controlledair pressure can be introduced into each chamber 1011. When the actuatoris put in operation by an ECU .[.4.]. .Iadd.300.Iaddend., the airpressure in each chamber 1011 can be varied to change the stiffness ofthe bush in a stepless manner. The stiffness of the bush can thus beappropriately changed to be high (hard) or (soft) after a shock at thefront wheel of a vehicle is detected.

FIGS. 33A-33G show a construction of a stabilizer as the third example.FIG. 33A shows a exploded perspective view of the torsion-bar-typestabilizer built in the axle-type rear suspension of an automobile.FIGS. 33B and 33C show enlarged partial longitudinal sectional views ofthe main part of the stabilizer in the coupled and uncoupled statesthereof. FIG. 33D shows an perspective view of the main part shown inFIGS. 33B and 33C and removed of a clutch. FIG. 33E shows a plan view ofthe main part shown in FIG. 33D. FIG. 33F shows a sectional view along aline XXXIIIF--XXXIIIF shown in FIG. 33B. FIG. 33G shows a sectional viewalong a line XXXIIIG--XXXIIIG shown in FIG. 33B. An axle 1103 coupledwith wheels 1102 is rotatably supported by an axle housing 1101. A pairof brackets 1104 and 1105 are secured on the axle housing 1101, inpositions separated from each other in the direction of the width of theautomobile. The torsion-bar-type stabilizer 1106 is coupled to bushesnot shown in the drawings. The stabilizer 1106 includes a right portion1107 and the left portion 1108 .Iadd.that .Iaddend.can be selectivelycoupled to each other integrally by a coupling unit 1109. A protrusion1117 and a hole 1118, which extend along an axis 1116, are formed at theends 1114 and 1115 of rods 1110 and 1112 opposite arms 1111 and 1113,and are provided with a male screw and a female screw which are engagedwith each other to couple the rods 1110 and 1112 rotatably relative toeach other around the axis 1116. The tips of the arms 1111 and 1113 arecoupled to brackets 1123 and 1124 secured on the side frames 1121 and1122 of the vehicle, by links 1119 and 1120. The coupling unit 1109includes the cylindrical clutch 1125, a clutch guide 1126 which isprovided at one end 1114 of the rod 1110 and supports the clutch 1125unrotatably relative to the guide around the axis 1116 but movably backand forth along the axis, and a clutch bearer 1127 which is provided atthe end 1115 of the rod 1112 and bears the clutch 1125 unrotatablyrelative to the bearer around the axis 1116. The inside circumferentialsurface of the clutch 1125 includes planes 1128 and 1129 facing eachother across the axis 1116 and extending in parallel with each otheralong the axis, the partially cylindrical surfaces 1130 and 1131adjoining the planes in positions opposed to each other across the axis1116, as shown in FIGS. 33F and 33G. Corresponding to the insidecircumferential surface of the clutch 1125, the peripheral surface ofthe clutch guide 1126 includes planes 1132 and 1133 facing each otheracross the axis 1116 and extending in parallel with each other acrossthe axis, and partially cylindrical surfaces 1134 and 1135 adjoining theplanes in position opposed to each other axis 1116. The peripheralsurface of the clutch bearer 1127 includes planes 1136 and 1137 facingeach other across the axis 1116 and extending in parallel with eachother along the axis, and partially cylindrical surfaces 1138 and 1139are always engaged with those 1128 and 1129 of the clutch 1125. When theclutch 1125 is in a position shown in FIG. 33C, the planes 1136 and 1137of the clutch bearer 1127 are also engaged with those 1129 and 1128 sothat the right portion 1107 and left portion 1108 of the stabilizer areintegrally coupled to each other rotatably relative to each other aroundthe axis 1116. The ends of the planes 1136 and 1137 of the clutch bearer1127 at the right portion 1107 of the stabilizer are chamfered at 1140and 1141 so that even if the rods 1110 and 1112 are slightly rotatedrelative to each other around the axis 1116, the clutch 1125 can bemoved from a position shown in FIG. 33B to a position shown in FIG. 33C,to couple the right portion 1107 and left portion 1108 of the stabilizerintegrally to each other as the arms 1111 and 1113 of the portions areon the same plane. The clutch 1125 is moved back and forth along theaxis 1116 by an actuator 1142 regulated by an ECU 300. The actuator 1142includes a hydraulic piston-cylinder unit 1143 secured on a differentialcasing not shown in the drawings, and a shifting fork 1149 whichincludes arms 1146 and 1147 engaged in the grooves 1144 and 1145 of theperipheral surface of the clutch .[.1225.]. .Iadd.1125.Iaddend., asshown in FIG. 33G, and is coupled to the piston rod 1148 of thepiston-cylinder unit 1143. When the clutch 1125 is placed in a positionshown in FIG. 33C, by the actuator 1142 according to an instruction fromthe ECU 300, the right portion 1107 and left portion 1108 of thestabilizer 1016 are integrally coupled to each other to put thestabilizer in such a state that it can fulfill its function to reducedthe rolling of the vehicle to improve its controllability and stability.When the clutch 1125 is placed in a position shown in FIG. 33B, by theactuator 1142, the right portion 1107 and left portion 1108 of thestabilizer .[.1016.]. .Iadd.1106 .Iaddend.can be rotated relative toeach other around the axis 1116 to reduce the shock on the vehicle,particularly the shock on its wheels on only one side of the vehicle, orimprove the feeling of ride of the vehicle.

FIGS. 34A and 34B show another stabilizer as the fourth example. Astabilizer-bar-type assembly 1310 includes a first stabilizer bar 1318and a second stabilizer bar 1320, as shown in FIG. 34A. The firststabilizer bar 1318 includes a main portion 1322 and an arm 1323. Themain portion 1322 is attached to the body of a vehicle by a pair offitting metals .[.1325.]. .Iadd.1324 .Iaddend.so that the main portion1322 can be twisted around its axis. The second stabilizer bar 1320 ishollow so that the main portion 1322 of the first stabilizer bar 1318extends through the second stabilizer bar, as shown in FIG. 34B. Thesecond stabilizer bar .[.1232.]. .Iadd.1320 .Iaddend.is disposed insidethe pair of fitting metals 1324 so that the first stabilizer bar 1318can be connected to and disconnected from the second stabilizer. Apiston 1330 on which a spool 1328 is secured is slidably disposed insideone end of the second stabilizer bar 1320 in such a manner that thepiston is liquid-tightly sealed by a sealing member 1332. The spool 1328is liquid-tightly sealed by a sealing member 1334, and projects out ofthe second stabilizer bar 1320. The spool 1328 has splines 1336 near thepistons 1330, while the second stabilizer bar 1320 has, at one end,splines 1338 which can be engaged with the splines 1336. The spool 1328has other splines 1340 inside the outwardly projecting end of the spool.A coupler 1344 is connected to the main portion 1322 of the firststabilizer bar 1318 by splines 1342. Splines 1346, which can be engagedwith the splines 1340, are provided on the coupler 1344 at the endopposed to the spool 1328. The coupler 1344 is connected to a mountingmetal 1324 through a rubber bush 1345, as shown in FIG. 34B, so that themain portion 1322 of the first stabilizer bar 1318 is twisted bydeforming the .Iadd.rubber bush 1345. The .Iaddend.coupler 1344 isfitted in such a position that the splines 1340 are engaged with thesplines 1346 when the spool 1328 is moved leftward as to the drawingsand the splines 1336 are engaged with the splines 1338. A bellowslikeboot 1347 for protecting the splines 1340 and 1346 from dust is providedbetween the coupler 1344 and the second stabilizer bar 1320. Two ports1348 and 1350 are provided in the second stabilizer bar 1320 in such amanner that the piston 1330 is located between the ports. Piping isprovided to lead a pressure fluid to the ports 1348 and 1350 in use.When the pressure fluid is led to one port 1350 through an actuator suchas a pressure control valve, the piston 1330 is moved leftward as to thedrawings, together with the spool 1328, the splines 1336 are engagedwith the splines 1338, and the splines 1340 are engaged with the splines1346. As a result, the first and the second stabilizer bars 1318 and1320 are coupled to each other so that the stiffness of the stabilizerbar assembly is heightened. When the pressure fluid is led to the otherport 1348, the piston 1330 is moved rightward and the splines aredisengaged from each other. As a result, the stiffness of the stabilizerbar assembly is constituted by only that of the first stabilizer bar1318.

FIGS. 35A, 35B and 35C show still another stabilizer as the fifthexample. FIG. 35A shows a plan view of the outline of the stabilizer1410. Wheels 1411 and suspension arms 1412 are also shown in FIG. 35A. Amain part 1414, a pair of arms 1412 are also shown in FIG. 35A. A mainpart 1414, a pair of arms 1416 and elongation means 1418 are provided.The main part 1414 like a round bar is laid through the bearing portions1421 of a pair of links 1420 disposed at a distance from each other inthe direction of the width of the body 1424 of a vehicle, and issupported by the bearing portions 1421 so that the main part 1414 can betwisted around its axis. The other bearing portions 1422 of the links1420 at the upper ends are rotatably supported by pins 1428 extendingthrough brackets 1426 welded on the vehicle body 1424. As a result, themain part 1414 is disposed along the width of the vehicle body, and canbe twisted relative to the vehicle body. The pair of arms 1416 are madeof flat bars. The first ends 1430 of the arms 1416 are coupled to theends of the main part 1414 by bolts and nuts 1432 so that the arms canbe turned about vertical axes. The second ends 1431 of the arms 1416 arelocated at a distance from the first ends 1430 in the front-to-reardirection of the vehicle body 1424. The front-to-rear direction includesan oblique longitudinal direction. the second ends 1431 of the arms 1416are displaced in the direction of the width of the vehicle body 1424 bythe elongation means 1418 made of power cylinders. Each of the powercylinders includes a cylinder 1434, a piston 1436 liquid-tightly andslidably fitted in the cylinder 1434, a piston rod 1438 coupled at oneend to the piston .[.1416.]. .Iadd.1436 .Iaddend.and projecting at theother end out of the cylinder 1434, and a included spring 1440 fordisplacing the piston 1436 in such a direction as to retract the pistonrod 1438. A stopper 1442 secured on the piston 1436 prevents the pistonfrom being displaced more than a predetermined quantity. The cylinder1434 is secured on the suspension arm 1412 in such a manner that thepiston rod 1438 is located more outside than the cylinder 1434 in thedirection of the width of the vehicle body. The second end 1431 of thearm 1416 is coupled to the outwardly projecting end of the piston rod1438 by a bolt and nut 1432 so that the arm 1416 can be turned about thevertical axis. One end of a flexible hose 1446 is connected to theliquid chamber 1444 of the cylinder 1434 opposite the side on which theincluded spring 1440 is located. The other end of the flexible hose 1446is connected to a pressure generator (not shown in the drawings) throughan actuator such as pressure control valve. Unless pressure is appliedto the liquid chambers 1444 of the power cylinders according to thestate of the actuator corresponding to an instruction from an ECU 300,the second end 1431 of the arms 1416 are located in inner positions asshown in FIG. 35A, so that the wheel rate of the stabilizer is low. Whenthe actuator is operated to apply pressure to the liquid chambers 1444of the power cylinders, the pressure acts to the pistons 1436 to pushout the piston rods 1438 against the compressed springs 1440. As aresult, the second ends 1431 of the arms 1416 are pushed out as shown byimaginary lines, i.e. double dotted lines, in FIG. 35A, to increase thearm ratio of the stabilizer to heighten its stiffness against therolling of the vehicle.

FIGS. 36A and 36B show a construction of a coupling unit for astabilizer and a lower control arm, as the sixth example. FIG. 36A showsa partial front view of a wishbone-type suspension including thecoupling unit for the stabilizer for a vehicle. FIG. 36B shows anenlarged sectional view of the coupling unit shown in FIG. 36A. A wheel1501 is rotatably supported by a knukcle 1503. The knuckle 1503 ispivotally coupled at the upper end to one end of an upper control arm1507 by a pivot 1505, and pivotally coupled at the other end to one endof the lower control arm 1511 by a pivot 1509. The upper control arm1507 and the lower control arm 1511 are pivotally coupled to the crossmember 1517 of the vehicle by pivots 1513 and 1515. The stabilizer 1518,which is shaped as U, is disposed along the width of the vehicle. Thestabilizer 1518 is coupled at its central rod 1519 to the body 1524 ofthe vehicle by brackets 1522 with rubber bushes not shown in thedrawings, so that the stabilizer can be turned about its axis. The tip1520a of the arm 1520 of the stabilizer 1518 is coupled to a point nearone end of the lower control arm 1511 by the coupling unit 1525. Thecoupling unit 1525 includes a piston-cylinder assembly 1526 composed ofa piston 1529 and a cylinder 1530 which define two cylinder chambers1527 and 1528. The cylinder 1530 includes an inner cylinder 1532 whichsupports the piston 1529 movably back and forth along an axis 1531, andouter cylinder 1533 disposed substantially concentrically to the innercylinder 1532, and end caps 1534 and 1535 which close both the ends ofthe inner cylinder and the outer cylinder. The piston 1529 includes amain portion 1536, and a piston 1537 which bears the main portion 1536at one end of the piston rod and extends along the axis .[.1131.]..Iadd.1531 .Iaddend.through the end cap .[.2534.]. .Iadd.1534.Iaddend.and the hole .[.2538.]. .Iadd.1538 .Iaddend.of the tip of thearm 1520 of the stabilizer 1518. A rubber bush 1540 and a retainer 1541for holding the bush are interposed between the shoulder 1539 of thepiston rod 1537 and the tip 1520a. A rubber bush 1543 and a retainer1544 are interposed between the tip 1520a and a nut 1542 screwed on thefront end of the piston rod 1537. As a result, the piston rod 1537 iscoupled to the tip 1520a of the arm 1520 of the stabilizer 1518 so thatan impulsive force is damped. A rod 1546, which extends along the axis1531 through a hole 1545 of the lower control arm 1511, is secured onthe end cap 1535. A rubber bush 1547 and a retainer 1548 for holding thebush are interposed between the end cap 1535 and the lower control arm1511. A rubber bush 1550 and a retainer 1551 for holding the bush areinterposed between the lower control arm 1511 and a nut 1549 screwed onthe front end of the rod 1546. As a result, the rod 1546 is coupled tothe lower control arm 1511 so that an impulsive force is damped. Theinner cylinder 1532 is provided with through holes 1552 and 1553 nearthe end caps 1534 and 1535. The end cap 1534 is integrally provided witha projection 1554 extending along the axis 1531 between the innercylinder 1532 and the outer cylinder 1533 and located in tight contactwith the inner and the outer cylinders. The projection 1554 has aninternal passage 1556 which is coincident at one end with the throughhole 1552 and is opened at the other end into an annular space 1555between the inner cylinder 1532 and the outer cylinder 1533. As aresult, the through hole 1552, the internal passage 1556, the annularspace 1555 and the other through hole 1553 constitute a passage meansfor connecting both the cylinder chambers 1527 and 1528 to each other. Aportion of the annular space 1555 is filled with air. Portions of thecylinder chambers 1527 and 1528, the internal passage 1556 and theannular 1555 are filled with oil. The change in the volume of the pistonrod 1537 in the cylinder 1530, which is caused by the displacement ofthe piston 1529 relative to the cylinder, is compensated by thecompression or expansion of the air filled in the portion of the annularspace 1555. The communication of the internal passage 1556 isselectively controlled by normally-opened solenoid valve 1557. Thesolenoid valve 1557 includes a housing 1559 containing a solenoid 1558and secured at one end on the outer cylinder 1533, a core 1561 supportedin the housing 1559 movably back and forth along an axis 1560, and acompressed helical spring 1562 for urging the core 1561 rightward as toFIG. 36B. A valve element 1563 is integrally provided at one end of thecore 1561 so that the valve element is selectively fitted into a hole1564 extending in the projection 1554 across the internal passage 1556.When no electricity is applied to the solenoid 1558 according to aninstruction from an ECU 300, the core 1561 is urged rightward as to thedrawing, by the compressed helical spring 1562, to open the valve 1557to allow the communication of the internal passage 1556. Whenelectricity is applied to the solenoid 1558 according to an instructionfrom the ECU 300, the core 1561 is driven leftward as to the drawings,against the force of the compressed helical spring 1562, to fit thevalve element 1563 into the hole 1564 to shut the internal passage 1556.At that time, the cylinder chambers 1527 and 1528 are disconnected fromeach other, and the oil in the cylinder chambers is kept from flowing tothe opposite cylinder chambers, so that the piston 1529 is hindered frommoving relative to the cylinder 1530 along the axis 1531. As a result,the stabilizer 1518 is put in such a state that it can fulfill itsfunction to suppress the rolling of the vehicle to improve thecontrollability and the stability of the vehicle as its wheel on oneside moves up on a bump of a road surface for the vehicle and down intoa hollow of a road surface. When no electricity is applied to thesolenoid 1558, the solenoid valve 1557 is maintained in an open positionshown in FIG. 36B, so that the oil in both the cylinder chambers 1527and 1528 can freely flow to the opposite cylinder chambers through aninternal passage 1556 and so forth. As a result, the piston 1529 canfreely move relative to the cylinder 1530 so that the tips of both theright and left arms 1520 can freely move relative to the correspondinglower control arms 1511. For that reason, the stabilizer does notfulfill its function, so that the shock at each rear wheel of thevehicle is reduced to keep the feel of a smooth ride of the vehicle.

What is claimed is:
 1. A rear suspension controller for a vehicle havinga suspension between a body and a rear wheel of the vehiclecomprising:front vehicle height detection means (e) for detecting adistance between a front wheel and the body of the vehicle and forgenerating a front vehicle height signal; a height data calculationmeans (f) for generating a plurality of height data from the frontvehicle height signal; a judgment means (g) for comparing each of theheight data with a reference value that is predetermined correspondingto each height datum and for generating a judgment result signaldepending on the results of the comparisons; and a rear suspensioncharacteristic alteration means (h) for altering the characteristic ofthe rear suspensions in receiving the judgment result signal.
 2. A rearsuspension controller as claimed in claim 1, wherein the rear suspensioncontroller further includes a vehicle speed detectiong means (M1) fordetecting the speed of the vehicle to generate a vehicle speed signal,anda reference alteration means (M7) for altering the reference valuesdepending on the vehicle speed signal.
 3. A rear suspension controlleras claimed in claim 2, wherein the height data .[.consists of.]..Iadd.comprises .Iaddend.an amplitude of the displacement and any one ofdisplacement of the vehicle height signal (VH(S)n) from the average, aspeed of the displacement and an acceleration of the displacement.
 4. Arear suspension controller as claimed in claim 2, wherein a plurality ofreference values (h1, h2, H1, H2) are predetermined in reference to eachheight datum (VHh-VH1, VHH-VHL), the judgment means generates aplurality of judgment result signals depending on the results of thecomparison between the height data and the respective reference valuesand the rear suspension characteristic alteration means alters thecharacteristic of the rear suspensions in a plurality of states (SOFT,SPORT, HARD) in response to the judgment result signals.
 5. A rearsuspension controller as claimed in claim 2, wherein the rear suspensioncharacteristic alteration means alters the characteristic of the rearsuspensions a delay time (Td) after receiving the judgment resultsignal, the delay time (Td) being calculated depending on the vehiclespeed signal (V).
 6. A rear suspension controller as claimed in claim 1,wherein the height data .[.consists of.]. .Iadd.comprises .Iaddend.anamplitude of the displacement and any one of the displacement of theaveraged vehicle height signal (VH(S)n) from the average, a speed of thedisplacement and an acceleration of the displacement.
 7. A rearsuspension controller as claimed in claim 1, wherein a plurality ofreference values (h1, h2, H1, H2) are predetermined corresponding toeach height datum (VHh-VHl, VHH-VHL), the judgment means generates aplurality of judgment result signals depending on the results of thecomparison between the height data and the respective reference valuesand the rear suspension characteristic alteration means alters thecharacteristic of the rear suspension in a plurality of states (SOFT,SPORT, HARD) in response to the judgment result signals.
 8. A rearsuspension controller as claimed in claim 1, wherein the rear suspensioncontroller includes a vehicle speed detection means (250) which detectsthe speed of the vehicle to generate a vehicle speed (V) and the rearsuspension characteristic alteration means alters the characteristic ofthe rear suspensions a delay time Td after receiving the judgment resultsignal, the delay time Td being calculated depending on the vehiclespeed signal (V). .Iadd.9. A rear suspension controller for a vehiclehaving a suspension between a body and a rear wheel of the vehicle,comprising:a front vehicle height detection means for detecting adistance between a front wheel and the body of the vehicle and forgenerating a front vehicle height signal; a judgment means for comparingthe height signal with a reference value and for generating a judgmentresult signal depending on the results of the comparison; a rearsuspension characteristic alteration means for altering thecharacteristic of the rear suspensions in receiving the judgment resultsignal; a vehicle speed detection means for detecting the speed of thevehicle to generate a vehicle speed signal; and a reference alterationmeans for altering the reference value depending on the vehicle speedsignal. .Iaddend. .Iadd.10. A rear suspension controller as claimed inclaim 9, wherein the rear suspension characteristic alteration meansalters the characteristic of the rear suspensions a delay time afterreceiving the judgment result signal, the delay time being calculateddepending on the vehicle speed signal. .Iaddend.